Arrayed waveguide grading with optical input and output characteristics settable to desired values

ABSTRACT

A waveguide device has an input waveguide, a plurality of output waveguides, a channel waveguide array, an input slab waveguide, and an output slab waveguide. The output slab waveguide connects an output end of the channel waveguide array to the output waveguide, and has optical input/output characteristics set to given ratios for the output waveguides with respect to the input waveguides. The waveguide device is capable of adjusting signal levels output from the respective waveguides without the need for circuit parts for compensating for loss differences and also the need for a process of highly accurately attaching parts.

The present Application is a Divisional Application of U.S. patentapplication Ser. No. 09/987,459 filed on Nov. 14, 2001 now U.S. Pat. No.6,679,748.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an arrayed waveguide grating or awaveguide device having a slab waveguide, a demultiplexer or amultiplexer which employs an arrayed waveguide grating or a waveguidedevice, and an optical communication system which employs an arrayedwaveguide grating or a waveguide device or a demultiplexer or amultiplexer.

2. Description of the Related Art

As the volume of data to be transmitted over an optical fibercommunication system increases, it is desired that the optical fibercommunication system have an increased capacity for data transmission.In view of such a demand, growing importance is attached to opticalwavelength filters for use as multiplexing and demultiplexing devicesfor multiplexing and demultiplexing wavelengths in DWDM (DenseWavelength Division Multiplexing) communication systems.

Optical wavelength filters are available in various types. Of thevarious wavelength filters, an arrayed waveguide grating (AWG) has anarrow wavelength band and a high extinction ratio, and has features asa multi-input, multi-output filter device. The arrayed waveguide gratingis capable of demultiplexing multiplexed signals and multiplexingsignals, and can easily be used to make up wavelength multiplexing anddemultiplexing devices.

FIG. 1 of the accompanying drawings shows an overall arrangement of aconventional arrayed waveguide grating. As shown in FIG. 1, theconventional arrayed waveguide grating, generally denoted by 11,comprises substrate 12, one or plural input waveguides 13 disposed onsubstrate 12, a plurality of output waveguides 14 disposed on substrate12, channel waveguide array 15 disposed on substrate 12,and curved in acertain direction with respective curvatures, inlet slab waveguide 16disposed on substrate 12, and connecting input waveguides 13 to channelwaveguide array 15, and outlet slab waveguide 17 disposed on substrate12, and connecting channel waveguide array 15 to output waveguides 14.Multiplexed signal light entered from input waveguides 13 is spread byinlet slab waveguide 16, and enters into channel waveguide array 15.

Channel waveguide array 15 comprises a plurality of arrayed waveguideshaving respective different optical path lengths which are successivelylonger or shorter. Therefore, signal light beams guided through therespective arrayed waveguides couple in respective different phasesspaced at certain intervals to the outlet slab waveguide 17. Since thesignal light beams actually suffer chromatic dispersion, the cophasalsurfaces of the signal light beams are inclined depending on thewavelength. As a result, the signal light beams are focused (converged)at different positions corresponding to the difference wavelengths onthe interface between the outlet slab waveguide 17 and the outputwaveguides 14. Since the output waveguides 14 are disposed in therespective positions corresponding to the difference wavelengths,desired wavelengths can be extracted from the respective outputwaveguides 14. The slab waveguides are disclosed in Japanese laid-openpatent publication No. 7-63934, for example. The general technique ofmultiplexing and demultiplexing optical signals is disclosed in Japaneselaid-open patent publication No. 7-49430, for example.

With the conventional arrayed waveguide grating 11 shown in FIG. 1, thelight emitted from channel waveguide array 15 into outlet slab waveguide17 reaches output waveguides 14 that is connected to the output side ofoutlet slab waveguide 17. In output waveguides 14, the intensity of thelight is greater progressively toward the central ones of outputwaveguides 14, and smaller progressively toward the peripheral ones ofoutput waveguides 14.

Heretofore, it has been proposed to uniformize the levels of the opticalsignals thereby to uniform the levels of the optical signals that aredetected from the output waveguides. According to one proposal, in orderto adjust the levels of the optical signals that are detected from theoutput waveguides, attenuators for compensating loss differences areindividually connected to the respective output waveguides, thus makingup an attenuator. However, it is necessary to prepare as many resistorshaving different resistances as the number of the different levels ofthe optical signals that are detected from the output waveguides.Furthermore, since the attenuation levels of the attenuators varydepending on the temperature, it is necessary to use a temperaturecompensation circuit in combination with the attenuators. The arrayedwaveguide grating with such attenuators for compensating lossdifferences is not practical as to cost and space.

An arrayed waveguide grating which is designed to extract a monitorsignal using higher-order diffracted light tends to cause a largedetected light level difference because a waveguide for guiding themonitor signal is positioned away from the optical axis of light emittedfrom a channel waveguide array. Consequently, the arrayed waveguidegrating needs a structure for compensating for a signal level lossbefore or after the signal light is detected.

Japanese laid-open patent publication No. 2000-98177 discloses a devicehaving an optical waveguide with a plurality of ports and an opticalfiber array. Deviations between the ports and the propagation axes ofthe optical fibers of the optical fiber array are managed to settransmission losses between the ports of the optical waveguide todesired values. Though the disclosed arrangement does not need anexternal attenuator, it poses yield and cost problems because of theneed for fine adjustment of the propagation axes.

While the drawbacks of the conventional arrayed waveguide gratings havebeen described above, multiplexers for multiplexing optical signals anddemultiplexers for demultiplexing optical signals which employ theconventional arrayed waveguide gratings, and optical communicationsystems which employ the conventional arrayed waveguide gratings and themultiplexers and demultiplexers are also problematic in that they arecomplex in structure and large in size, and cannot be reduced in cost.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an arrayedwaveguide grating which is capable of adjusting signal levels outputfrom respective waveguides without the need for circuit parts forcompensating for loss differences and also the need for a process ofhighly accurately attaching parts, and a multiplexer, a demultiplexer,and an optical communication system which use such an arrayed waveguidegrating.

According to a first aspect of the present invention, an arrayedwaveguide grating comprises: one or plural input waveguides forinputting signal lights; a plurality of output waveguides for outputtingsignal lights; a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences; aninput slab waveguide connecting an input end of the channel waveguidearray to the input waveguides; and an output slab waveguide connectingan output end of the channel waveguide array to the output waveguides,and having optical input/output characteristics set to predeterminedratios for the respective output waveguides with respect to the inputwaveguides.

The first aspect of the present invention is concerned with thedemultiplexing of light, and optical input/output characteristics areset to predetermined ratios for the respective output waveguides withrespect to the input waveguides. This makes it unnecessary to employexternal circuit parts for compensating for loss differences.

According to a second aspect of the present invention, an arrayedwaveguide grating comprises: one or plural input waveguides forinputting signal lights; a plurality of output waveguides for outputtingsignal lights; a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences; aninput slab waveguide connecting an input end of the channel waveguidearray to the input waveguides; and an output slab waveguide connectingan output end of the channel waveguide array to the output waveguides,and having optical input/output characteristics set to predeterminedratios for the respective output waveguides with respect to the inputwaveguides depending on the differences between optical losses alongrespective paths in the output slab waveguide.

The second aspect of the present invention is concerned with thedemultiplexing of light, optical loss differences are developed at aboundary of the slab waveguide for thereby setting optical input/outputcharacteristics predetermined ratios for the respective outputwaveguides with respect to the input waveguides. This makes itunnecessary to employ external circuit parts for compensating for lossdifferences.

According to a third aspect of the present invention, an arrayedwaveguide grating comprises: a plurality of input waveguides forinputting signal lights having different wavelengths each other; one orplural output waveguides for outputting signal lights; a channelwaveguide array having waveguides which are successively longer withpredetermined waveguide length differences; an output slab waveguideconnecting an output end of the channel waveguide array to the outputwaveguides; and an input slab waveguide connecting an input end of thechannel waveguide array to the input waveguides, and having opticalinput/output characteristics set to predetermined ratios for therespective input waveguides corresponding to the output waveguides.

Unlike the first aspect of the present invention, the third aspect ofthe present invention is concerned with the multiplexing of lights, andoptical input/output characteristics are set to predetermined ratios forthe respective input waveguides with respect to the output waveguides.This makes it unnecessary to employ external circuit parts forcompensating for loss differences.

According to a fourth aspect of the present invention, an arrayedwaveguide grating comprises: a plurality of input waveguides forinputting signal lights having different wavelengths each other; one orplural output waveguides for outputting signal lights; a channelwaveguide array having waveguides which are successively longer withpredetermined waveguide length differences; an output slab waveguideconnecting an output end of the channel waveguide array to the outputwaveguides; and an input slab waveguide connecting an input end of thechannel waveguide array to the input waveguides; and having opticalinput/output characteristics set to predetermined ratios for therespective input waveguides corresponding to the output waveguidesdepending on the differences between optical losses along respectivepaths in the output slab waveguide.

Unlike the second aspect of the present invention, the fourth aspect ofthe present invention is concerned with the multiplexing of lights, andoptical loss differences are developed at boundaries of the inputwaveguides and the slab waveguide for thereby setting opticalinput/output characteristics predetermined ratios for the respectiveinput waveguides with respect to the output waveguides. This makes itunnecessary to employ external circuit parts for compensating for lossdifferences.

According to a fifth aspect of the present invention, an arrayedwaveguide grating comprises: one or plural input waveguides forinputting signal lights; a plurality of output waveguides for outputtingsignal lights; a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences; aninput slab waveguide connecting an input end of the channel waveguidearray to the input waveguides; and an output slab waveguide connectingan output end of the channel waveguide array to the output waveguides,the output slab waveguide having a core layer disposed therein forpropagating light therethrough, the core layer being partly cut off inselected or all paths therein which interconnect the channel waveguidearray and the output waveguides, and a cladding layer disposed in cutregions of the core layer and on opposite sides of the core layer, thecut regions in the paths having cut lengths set to predetermined valuesin the direction in which the signal lights propagate, depending onoptical losses of the signal lights propagated in the paths.

With the fifth aspect of the present invention, the core layer of theslab waveguide is partly cut off as required, and the optical losseswith respect to the output waveguides at the time of demultiplexing thelight signal are adjusted based on the lengths of the cut regions.

According to a sixth aspect of the present invention, an arrayedwaveguide grating comprises: a plurality of input waveguides forinputting signal lights having different wavelengths each other; one orplural output waveguides for outputting signal lights; a channelwaveguide array having waveguides which are successively longer withpredetermined waveguide length differences; an output slab waveguideconnecting an output end of the channel waveguide array to the outputwaveguides; and an input slab waveguide connecting an input end of thechannel waveguide array to the input waveguides, the input slabwaveguide having a core layer disposed therein for propagating lighttherethrough, the core layer being partly cut off in selected or allpaths therein which interconnect the channel waveguide array and theinput waveguides, and a cladding layer disposed in cut regions of thecore layer and on opposite sides of the core layer, the cut regions inthe paths having cut lengths set to predetermined values in thedirection in which the signal lights propagate, depending on opticallosses of the signal lights propagated in the paths.

With the sixth aspect of the present invention, the core layer of theslab waveguide is partly cut off as required, and the optical losses ofthe signal lights to be multiplexed into the output waveguides areadjusted based on the lengths of the cut regions.

According to a seventh aspect of the present invention, an arrayedwaveguide grating comprises: one or plural input waveguides forinputting signal lights; a plurality of output waveguides for outputtingsignal lights; the output waveguides having at least one core layerdisposed therein for propagating light therethrough, the core layerbeing partly cut off, and a cladding layer disposed in cut regions ofthe core layer and on opposite sides of the core layer, the cut regionshaving cut lengths set to predetermined values depending on opticallosses of the signal lights propagated in the output waveguides; achannel waveguide array having waveguides which are successively longerwith predetermined waveguide length differences; an input slab waveguideconnecting an input end of the channel waveguide array to the inputwaveguides; and an output slab waveguide connecting an output end of thechannel waveguide array to the output waveguides.

With the seventh aspect of the present invention, whereas the core layerof the slab waveguide is partly cut off as required with the fifthaspect of the present invention, the core layer of some or all of theoutput waveguides for propagating the signal lights output from the slabwaveguide is partly cut off as required, and the optical losses withrespect to the output waveguides are adjusted based on the lengths ofthe cut regions.

According to an eighth aspect of the present invention, an arrayedwaveguide grating comprises: a plurality of input waveguides forinputting signal lights having different wavelengths each other, theinput waveguides having at least one core layer disposed therein forpropagating light therethrough, the core layer being partly cut off, anda cladding layer disposed in cut regions of the core layer and onopposite sides of the core layer, the cut regions having cut lengths setto predetermined values depending on optical losses of the signal lightspropagated in the input waveguides; one or plural output waveguides foroutputting signal lights; a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences, an input slab waveguide connecting an input end of thechannel waveguide array to the input waveguides; and an output slabwaveguide connecting an output end of the channel waveguide array to theoutput waveguides.

With the eighth aspect of the present invention, whereas the core layerof the slab waveguide is partly cut off as required with the sixthaspect of the present invention, the core layer of some or all of theinput waveguides for transmitting the signal lights into the slabwaveguide is partly cut off as required, and the optical losses withrespect to the input waveguides are adjusted based on the lengths of thecut regions.

According to a ninth aspect of the present invention, an arrayedwaveguide grating comprises: one or plural input waveguides forinputting signal lights; a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an input slab waveguide connecting an input end of thechannel waveguide array to the input waveguides; an output slabwaveguide connecting an output end of the channel waveguide array to theinput end thereof; and a plurality of output waveguides havingrespective ends connected to the output end of the output slabwaveguide, wherein selected or all of the ends of the output waveguideshave respective central positions displaced from corresponding focusedpositions in a direction perpendicular to central axes of the outputwaveguides by predetermined values depending on losses to be given tothe signal lights propagated in the output waveguides.

Usually, the focused positions located in the vicinity of the boundaryof the slab waveguide at its output end are aligned with the centralaxes of the output waveguides to increase the coupling efficiency. Withthe ninth aspect of the present invention, the central positions of theends of the output waveguides which face the slab waveguide aredisplaced from the corresponding focused positions in the directionperpendicular to the central axes of the output waveguides bypredetermined values depending on losses to be given to the signallights propagated in the output waveguides, thereby adjusting the lossesof the signal lights propagated in the output waveguides.

According to a tenth aspect of the present invention, an arrayedwaveguide grating comprises: a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an input slab waveguide having an output end connected toan input end of the channel waveguide array; one or plural outputwaveguides for outputting signal lights; an output slab waveguideconnecting an output end of the channel waveguide array to the outputwaveguides; and a plurality of input waveguides having respective endsconnected to the input end of the input slab waveguide, wherein selectedor all of the ends of the input waveguides have respective centralpositions displaced from corresponding focused positions in a directionperpendicular to central axes of the input waveguides by predeterminedvalues depending on losses to be given to the signal lights propagatedin the output waveguides.

Usually, the central axis of an output waveguide for extracting amultiplexed signal is aligned with the optical axe of the multiplexedsignal coupled to the output waveguide to increase the total efficiency.With the tenth aspect of the present invention, the input waveguides aredisplaced in the direction perpendicular to the central axes thereof toshift the propagation axes of the signal lights coupled to the outputwaveguides depending on losses to be given to the signal lightspropagated in the output waveguides. The losses of the signal lightspropagated in the output waveguides are adjusted based on the distancesby which the input waveguides are displaced.

According to an eleventh aspect of the present invention, an arrayedwaveguide grating comprises: a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an input slab waveguide having an output end connected toan input end of the channel waveguide array; one or plural inputwaveguides for inputting signal lights, the input waveguides havingoutput ends connected to an input end of the input slab waveguide; anoutput slab waveguide having an input end connected to an output end ofthe channel waveguide array; and a plurality of output waveguides havingrespective ends connected to the output end of the output slabwaveguide, wherein selected or all of central axes of the outputwaveguides are inclined at the interconnected points of the outputwaveguides and the channel waveguide array at respective anglesdepending on losses to be given to the signal lights coupled at theinterconnected points.

With the eleventh aspect of the present invention, the angles betweenthe central axes of the output waveguides for extracting demultiplexedsignal lights and the propagation axes of the demultiplexed signallights coupled to the respective output waveguides are set depending onlosses to be given to the signal lights, for thereby adjusting thelosses of the signal lights propagated in the output waveguides.

According to a twelfth aspect of the present invention, an arrayedwaveguide grating comprises: a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an input slab waveguide having an output end connected toan input end of the channel waveguide array; one or plural outputwaveguides for outputting signal lights; an output slab waveguideconnecting an output end of the channel waveguide array to the outputwaveguides; and a plurality of input waveguides having respective endsconnected to the input end of the input slab waveguide, wherein selectedor all of central axes of the input waveguides are inclined at theinterconnected points of the input waveguides and the input slabwaveguide at respective angles depending on losses to be given to thesignal lights coupled at the interconnected points.

With the twelfth aspect of the present invention, the angles between theends of the input waveguides and the input slab waveguide array and thecentral axes of the input waveguides set depending on losses to be givento the signal lights, for thereby adjusting the losses of the signallights transmitted respectively from input waveguides.

According to a thirteenth aspect of the present invention, an arrayedwaveguide grating comprises: a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an input slab waveguide having an output end connected toan input end of the channel waveguide array; one or plural inputwaveguides for inputting signal lights, the input waveguides havingoutput ends connected to an input end of the input slab waveguide; anoutput slab waveguide having an input end connected to an output end ofthe channel waveguide array; and a plurality of output waveguides havingrespective ends connected to the output end of the output slabwaveguide, wherein selected or all widths of the output waveguides atends thereof are set to predetermined values depending on losses to begiven to the signal lights.

With the thirteenth aspect of the present invention, the widths, in thedirection perpendicular to the propagation axes, of selected or all ofthe output waveguides at their portions connected to the output slabwaveguide are set to values depending on losses to be given to thesignal lights, for thereby adjusting the losses of the signal lightspropagated in the output waveguides.

According to a fourteenth aspect of the present invention, an arrayedwaveguide grating comprises: a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an input slab waveguide having an output end connected toan input end of the channel waveguide array; one or plural outputwaveguides for outputting signal lights; an output slab waveguideconnecting an output end of the channel waveguide array to the outputwaveguides; and a plurality of input waveguides having respective endsconnected to the input end of the input slab waveguide, wherein selectedor all widths of the input waveguides at ends thereof are set topredetermined values depending on losses to be given to the signallights.

With the fourteenth aspect of the present invention, the widths, in thedirection perpendicular to the propagation axes, of selected or all ofthe input waveguides at their portions connected to the input slabwaveguide are set to values depending on losses to be given to thesignal lights, for thereby adjusting the losses of the signal lightspropagated in the input waveguides.

According to a fifteenth aspect of the present invention, an arrayedwaveguide grating comprises: a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an input slab waveguide having an output end connected toan input end of the channel waveguide array; one or plural inputwaveguides for inputting signal-lights, the input waveguides havingoutput ends connected to an input end of the input slab waveguide; anoutput slab waveguide having an input end connected to an output end ofthe channel waveguide array; and a plurality of output waveguides havingrespective ends connected to the output end of the output slab waveguidewherein the ends of the output waveguides and the channel waveguidearray are displaced in the direction of propagation axes of the outputwaveguides depending on losses to be given to the signal lightspropagated from the channel waveguide array to the ends of the outputwaveguides.

Usually, the focused positions located in the vicinity of the boundaryof the slab waveguide at its output end are aligned with the centralaxes of the output waveguides to increase the coupling efficiency to theoutput waveguides. With the fifteenth aspect of the present invention,the lengths between the ends of the output waveguides and the focusedpositions are displaced, for some or all of the output waveguides, inthe direction of propagation axes of the output waveguides depending onlosses to be given to the signal lights propagated to the outputwaveguides, for thereby adjusting the losses of the signal lightspropagated in the output waveguides.

According to a sixteenth aspect of the present invention, an arrayedwaveguide grating comprises: a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an input slab waveguide having an output end connected toan input end of the channel waveguide array; one or plural outputwaveguides for outputting signal lights; an output slab waveguideconnecting an output end of the channel waveguide array to the outputwaveguides; and a plurality of input waveguides having respective endsconnected to the input end of the input slab waveguide, wherein thelengths between the ends of the input waveguides and the channelwaveguide array are displaced in the direction of propagation axes ofthe input waveguides depending on losses to be given to the signallights propagated from the channel waveguide array to the ends of theinput waveguides.

Usually, the focused positions located in the vicinity of the boundaryof the output slab waveguide and the ends of the output waveguides arealigned to increase the coupling efficiency of the signal lights whichare propagated from the input waveguides through the channel waveguidearray to the output slab waveguide. With the sixteenth aspect of thepresent invention, some or all of the input waveguides are displacedfrom their normal positions in the direction of the propagation axesdepending on losses to be given to the signal lights, for therebyadjusting the losses of the signal lights.

According to a seventeenth aspect of the present invention, ademultiplexer comprises: an arrayed waveguide grating comprising one orplural input waveguides for inputting signal lights; a plurality ofoutput waveguides for outputting signal lights; a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences; an input slab waveguide connecting aninput end of the channel waveguide array to the input waveguides; and anoutput slab waveguide connecting an output end of the channel waveguidearray to the output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to the input waveguides; and level adjustingmeans for being supplied with the signal lights of respectivewavelengths from the output waveguides of the arrayed waveguide grating,and adjusting output levels of the signal lights to desired values.

With the seventeenth aspect of the present invention, the arrayedwaveguide grating itself sets the optical input/output characteristicsto predetermined ratios for the respective output waveguides withrespect to the input waveguides, and the level adjusting means issupplied with the signal lights of respective wavelengths from theoutput waveguides and adjusts output levels of the signal lights todesired values. The input/output characteristics can thus be made flator freely adjusted depending on an apparatus or system with which thedemultiplexer is used.

According to an eighteenth aspect of the present invention, ademultiplexer comprises: an arrayed waveguide grating comprising one orplural input waveguides for inputting signal lights, a plurality ofoutput waveguides for outputting signal lights, a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences, an input slab waveguide connecting aninput end of the channel waveguide array to the input waveguides, and anoutput slab waveguide connecting an output end of the channel waveguidearray to the output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to the input waveguides depending on thedifferences between optical losses along respective paths in the outputslab waveguide; and level adjusting means for being supplied with thesignal lights of respective wavelengths from the output waveguides ofthe arrayed waveguide grating, and adjusting output levels of the signallights to desired values.

With the eighteenth aspect of the present invention, the arrayedwaveguide grating itself sets the optical input/output characteristicsto predetermined ratios for the respective output waveguides withrespect to the input waveguides based on optical loss differences at theboundary of the slab waveguide, and the level adjusting means issupplied with the signal lights of respective wavelengths from theoutput waveguides and adjusts output levels of the signal lights todesired values. The input/output characteristics-can thus be made flator freely adjusted depending on an apparatus or system with which thedemultiplexer is used.

According to a nineteenth aspect of the present invention, a multiplexercomprises: a plurality of light sources; an arrayed waveguide gratingcomprising a plurality of input waveguides for inputting signal lightshaving different wavelengths each other, one or plural output waveguidesfor outputting signal lights, a channel waveguide array havingwaveguides which are successively longer with predetermined waveguidelength differences, an output slab waveguide connecting an output end ofthe channel waveguide array to the output waveguides, and an input slabwaveguide connecting an input end of the channel waveguide array to theinput waveguides, and having optical input/output characteristics set topredetermined ratios for the respective input waveguides correspondingto the output waveguides; level detecting means for detecting levels ofthe signal lights input from the light sources to the arrayed waveguidegrating; and level adjusting means for comparing the levels of thesignal lights detected by the level detecting means with predeterminedlevels for the respective wavelengths, and adjusting output levels ofthe light sources to set the levels of the waveguides multiplexed by thearrayed waveguide grating to desired values.

With the nineteenth aspect of the present invention, the arrayedwaveguide grating itself sets the optical input/output characteristicsto predetermined ratios for the respective input waveguides with respectto the output waveguides, and the levels of the signal lights input fromthe light sources to the arrayed waveguide grating are detected by thelevel detecting means. By adjusting the output levels of the lightsources, the levels of the signal lights of the respective wavelengthswhich have been multiplexed by the arrayed waveguide grating are set todesired values. The input/output characteristics can thus be made flator freely adjusted at the output waveguides depending on an apparatus orsystem with which the demultiplexer is used.

According to a twentieth aspect of the present invention, a multiplexercomprises: a plurality of light sources; an arrayed waveguide gratingcomprising a plurality of input waveguides for inputting signal lightshaving different wavelengths each other, one or plural output waveguidesfor outputting signal lights, a channel waveguide array havingwaveguides which are successively longer with predetermined waveguidelength differences, an output slab waveguide connecting an output end ofthe channel waveguide array to the output waveguides, and an input slabwaveguide connecting an input end of the channel waveguide array to theinput waveguides, and having optical input/output characteristics set topredetermined ratios for the respective input waveguides correspondingto the output waveguides depending on the differences between opticallosses along respective paths in the output slab waveguide; leveldetecting means for detecting levels of the signal lights input from thelight sources to the arrayed waveguide grating; and level adjustingmeans for comparing the levels of the signal lights detected by thelevel detecting means with predetermined levels for the respectivewavelengths, and adjusting output levels of the light sources to set thelevels of the waveguides multiplexed by the arrayed waveguide grating todesired values.

With the twentieth aspect of the present invention, the arrayedwaveguide grating itself sets the optical input/output characteristicsto predetermined ratios for the respective input waveguides with respectto the output waveguides based on optical loss differences at theboundary of the slab waveguide, and the levels of the signal lightsinput from the light sources to the arrayed waveguide grating aredetected by the level detecting means. By adjusting the output levels ofthe light sources, the levels of the signal lights of the respectivewavelengths which have been multiplexed by the arrayed waveguide gratingare set to desired values. The input/output characteristics can thus bemade flat or freely adjusted at the output waveguides depending on anapparatus or system with which the demultiplexer is used.

According to a twenty-first aspect of the present invention, an opticalcommunication system comprises: optical transmitting means fortransmitting optical signals of respective wavelengths parallel to eachother; a multiplexer for wavelength-division multiplexing the opticalsignals of respective wavelengths transmitted by the light transmittingmeans; an optical transmission path for transmitting awavelength-division multiplexed optical signal output from themultiplexer; a node disposed in the optical transmission path and havingan arrayed waveguide grating; a demultiplexer for being supplied withthe optical signal transmitted over the optical transmission path viathe node and demultiplexing the optical signal into the optical signalsof respective wavelengths; and optical receiving means for receiving theoptical signals of respective wavelengths demultiplexed by thedemultiplexer; the multiplexer comprising an arrayed waveguide gratingcomprising a plurality of input waveguides for inputting signal lightshaving different wavelengths each other, one or plural output waveguidesfor outputting signal lights, a channel waveguide array havingwaveguides which are successively longer with predetermined waveguidelength differences, an output slab waveguide connecting an output end ofthe channel waveguide array to the output waveguides, and an input slabwaveguide connecting an input end of the channel waveguide array to theinput waveguides, and having optical input/output characteristics set topredetermined ratios for the respective input waveguides correspondingto the output waveguides; the demultiplexer comprising an arrayedwaveguide grating comprising one or plural input waveguides forinputting signal lights, a plurality of output waveguides for outputtingsignal lights, a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences, aninput slab waveguide connecting an input end of the channel waveguidearray to the input waveguides, and an output slab waveguide connectingan output end of the channel waveguide array to the output waveguides,and having optical input/output characteristics set to predeterminedratios for the respective output waveguides with respect to the inputwaveguides.

With the twenty-first aspect of the present invention, the opticalcommunication system, which is of an linear type, comprises opticaltransmitting means, a multiplexer for wavelength-division multiplexingthe optical signals of respective wavelengths transmitted by the lighttransmitting means, an optical transmission path for transmitting amultiplexed optical signal output from the multiplexer, a node disposedin the optical transmission path and having an arrayed waveguidegrating, a demultiplexer for being supplied with the optical signaltransmitted over the optical transmission path via the node anddemultiplexing the optical signal into the optical signals of respectivewavelengths, and optical receiving means for receiving the opticalsignals of respective wavelengths demultiplexed by the demultiplexer.The multiplexer comprises an arrayed waveguide grating according to thethird aspect and sets optical input/output characteristics topredetermined ratios for the respective input waveguides correspondingto the output waveguides, and the demultiplexer comprises an arrayedwaveguide grating according to the first aspect and sets opticalinput/output characteristics to predetermined ratios for the respectiveoutput waveguides with respect to the input waveguides.

According to a twenty-second aspect of the present invention, an opticalcommunication system comprises: optical transmitting means fortransmitting optical signals of respective wavelengths parallel to eachother; a multiplexer for wavelength-division multiplexing the opticalsignals of respective wavelengths transmitted by the light transmittingmeans; an optical transmission path for transmitting awavelength-division multiplexed optical signal output from themultiplexer, a node disposed in the optical transmission path and havingan arrayed waveguide grating; a demultiplexer for being supplied withthe optical signal transmitted over the optical transmission path viathe node and demultiplexing the optical signal into the optical signalsof respective wavelengths; and optical receiving means for receiving theoptical signals of respective wavelengths demultiplexed by thedemultiplexer; the multiplexer comprising an arrayed waveguide gratingcomprising a plurality of input waveguides for inputting signal lightshaving different wavelengths each other, one or plural output waveguidesfor outputting signal lights, a channel waveguide array havingwaveguides which are successively longer with predetermined waveguidelength differences, an output slab waveguide connecting an output end ofthe channel waveguide array to the output waveguides, and an input slabwaveguide connecting an input end of the channel waveguide array to theinput waveguides, and having optical input/output characteristics set topredetermined ratios for the respective input waveguides correspondingto the output waveguides depending on the differences between opticallosses along respective paths in the output slab waveguide; thedemultiplexer comprising an arrayed waveguide grating comprising one orplural input waveguides for inputting signal lights, a plurality ofoutput waveguides for outputting signal lights, a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences, an input slab waveguide connecting aninput end of the channel waveguide array to the input waveguides, and anoutput slab waveguide connecting an output end of the channel waveguidearray to the output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to the input waveguides depending on thedifferences between optical losses along respective paths in the outputslab waveguide.

With the twenty-second aspect of the present invention, the opticalcommunication system, which is of an linear type, comprises opticaltransmitting means, a multiplexer for wavelength-division multiplexingthe optical signals of respective wavelengths transmitted by the lighttransmitting means, an optical transmission path for transmitting amultiplexed optical signal output from the multiplexer, a node disposedin the optical transmission path and having an arrayed waveguidegrating, a demultiplexer for being supplied with the optical signaltransmitted over the optical transmission path via the node anddemultiplexing the optical signal into the optical signals of respectivewavelengths, and optical receiving means for receiving the opticalsignals of respective wavelengths demultiplexed by the demultiplexer.The multiplexer comprises an arrayed waveguide grating according to thefourth aspect and sets optical input/output characteristics topredetermined ratios for the respective input waveguides correspondingto the output waveguides, and the demultiplexer comprises an arrayedwaveguide grating according to the second aspect and sets opticalinput/output characteristics to predetermined ratios for the respectiveoutput waveguides with respect to the input waveguides.

According to a twenty-third aspect of the present invention, an opticalcommunication system comprises: an annular transmission path having aplurality of nodes interconnected in a ring by a transmission path, fortransmitting a multiplexed optical signal over the transmission path;each of the nodes having a first arrayed waveguide grating fordemultiplexing a multiplexed optical signal into optical signals ofrespective wavelengths, and a second arrayed waveguide grating formultiplexing the demultiplexed optical signals of respectivewavelengths; the first arrayed waveguide grating comprising one orplural input waveguides for inputting signal lights, a plurality ofoutput waveguides for outputting signal lights, a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences, an input slab waveguide connecting aninput end of the channel waveguide array to the input waveguides, and anoutput slab waveguide connecting an output end of the channel waveguidearray to the output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to the input waveguides; the second arrayedwaveguide grating comprising a plurality of input waveguides forinputting signal lights having different wavelengths each other, one orplural output waveguides for outputting signal lights, a channelwaveguide array having waveguides which are successively longer withpredetermined waveguide length differences, an output slab waveguideconnecting an output end of the channel waveguide array to the outputwaveguides, and an input slab waveguide connecting an input end of thechannel waveguide array to the input waveguides, and having opticalinput/output characteristics set to predetermined ratios for therespective input waveguides corresponding to the output waveguides.

With the twenty-third aspect of the present invention, the opticalcommunication system, which is of an annular type, comprises an annulartransmission path having a plurality of nodes interconnected in a ringby a transmission path, for transmitting a multiplexed optical signalover the transmission path, each of the nodes having a first arrayedwaveguide grating for demultiplexing a multiplexed optical signal intooptical signals of respective wavelengths, and a second arrayedwaveguide grating for multiplexing the demultiplexed optical signals ofrespective wavelengths. The first arrayed waveguide grating comprises anarrayed waveguide grating according to the third aspect and sets opticalinput/output characteristics to predetermined ratios for the respectiveoutput waveguides connected to the output end of the slab waveguide withrespect to the input waveguides. The second arrayed waveguide gratingcomprises an arrayed waveguide grating according to the first aspect andsets optical input/output characteristics to predetermined ratios forthe respective input waveguides corresponding to the output waveguides.

According to a twenty-fourth aspect of the present invention, an opticalcommunication system comprises: an annular transmission path having aplurality of nodes interconnected in a ring by a transmission path, fortransmitting a multiplexed optical signal over the transmission path;each of the nodes having a first arrayed waveguide grating fordemultiplexing a multiplexed optical signal into optical signals ofrespective wavelengths, and a second arrayed waveguide grating formultiplexing the demultiplexed optical signals of respectivewavelengths; the first arrayed waveguide grating comprising one orplural input waveguides for inputting signal lights, a plurality ofoutput waveguides for outputting signal lights, a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences, an input slab waveguide connecting aninput end of the channel waveguide array to the input waveguides, and anoutput slab waveguide connecting an output end of the channel waveguidearray to the output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to the input waveguides depending on thedifferences between optical losses along respective paths in the outputslab waveguide; the second arrayed waveguide grating comprising aplurality of input waveguides for inputting signal lights havingdifferent wavelengths each other, one or plural output waveguides foroutputting signal lights, a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences, an output slab waveguide connecting an output end of thechannel waveguide array to the output waveguides, and an input slabwaveguide connecting an input end of the channel waveguide array to theinput waveguides, and having optical input/output characteristics set topredetermined ratios for the respective input waveguides correspondingto the output waveguides depending on the differences between opticallosses along respective paths in the output slab waveguide.

With the twenty-fourth aspect of the present invention, the opticalcommunication system, which is of an annular type, comprises an annulartransmission path having a plurality of nodes interconnected in a ringby a transmission path, for transmitting a wavelength-divisionmultiplexed optical signal over the transmission path, each of the nodeshaving a first arrayed waveguide grating for demultiplexing awavelength-division multiplexed optical signal into optical signals ofrespective wavelengths, and a second arrayed waveguide grating forwavelength-division multiplexing the demultiplexed optical signals ofrespective wavelengths. The first arrayed waveguide grating comprises anarrayed waveguide grating according to the fourth aspect and setsoptical input/output characteristics to predetermined ratios for therespective output waveguides connected to the output end of the slabwaveguide with respect to the input waveguides. The second arrayedwaveguide grating comprises an arrayed waveguide grating according tothe second aspect and sets optical input/output characteristics topredetermined ratios for the respective input waveguides correspondingto the output waveguides.

According to a twenty-fifth aspect of the present invention, an opticalcommunication system comprises: optical transmitting means fortransmitting optical signals of respective wavelengths parallel to eachother; a multiplexer for multiplexing the optical signals of respectivewavelengths transmitted by the light transmitting means; an opticaltransmission path for transmitting a multiplexed optical signal outputfrom the multiplexer; a node disposed in the optical transmission path;a demultiplexer for being supplied with the optical signal transmittedover the optical transmission path via the node and demultiplexing theoptical signal into the optical signals of respective wavelengths; andoptical receiving means for receiving the optical signals of respectivewavelengths demultiplexed by the demultiplexer; the multiplexercomprising an arrayed waveguide grating having a plurality of inputwaveguides for inputting signal lights having different wavelengths eachother, one or plural output waveguides for outputting signal lights, achannel waveguide array having waveguides which are successively longerwith predetermined waveguide length differences, an output slabwaveguide connecting an output end of the channel waveguide array to theoutput waveguides, and an input slab waveguide connecting an input endof the channel waveguide array to the input waveguides, and havingoptical input/output characteristics set to predetermined ratios for therespective input waveguides corresponding to the output waveguides,level detecting means for detecting levels of the signal lights input tothe arrayed waveguide grating, and level adjusting means for comparingthe levels of the signal lights detected by the level detecting meanswith predetermined levels for the respective wavelengths, and adjustingoutput levels of the light signals to set the levels of the waveguidesmultiplexed by the arrayed waveguide grating to desired values; thedemultiplexer comprising an arrayed waveguide grating comprising one orplural input waveguides for inputting signal lights, a plurality ofoutput waveguides for outputting signal lights, a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences, an input slab waveguide connecting aninput end of the channel waveguide array to the input waveguides, and anoutput slab waveguide connecting an output end of the channel waveguidearray to the output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to the input waveguides, and level adjustingmeans for being supplied with the signal lights of respectivewavelengths from the output waveguides of the arrayed waveguide grating,and adjusting output levels of the signal lights to desired values.

With the twenty-fifth aspect of the present invention, the opticalcommunication system, which is of a linear type, comprises opticaltransmitting means, a multiplexer for wavelength-division multiplexingthe optical signals of respective wavelengths transmitted by the lighttransmitting means, an optical transmission path for transmitting awavelength-division multiplexed optical signal output from themultiplexer, a node disposed in the optical transmission path, ademultiplexer for being supplied with the optical signal transmittedover the optical transmission path via the node and demultiplexing theoptical signal into the optical signals of respective wavelengths, andoptical receiving means for receiving the optical signals of respectivewavelengths demultiplexed by the demultiplexer. The multiplexercomprises a device according to the nineteenth aspect, and thedemultiplexer comprises a device according to the seventeenth aspect,thus setting optical input/output characteristics to predeterminedratios.

According to a twenty-sixth aspect of the present invention, an opticalcommunication system comprises: optical transmitting means fortransmitting optical signals of respective wavelengths parallel to eachother; a multiplexer for multiplexing the optical signals of respectivewavelengths transmitted by the light transmitting means; an opticaltransmission path for transmitting a multiplexed optical signal outputfrom the multiplexer; a node disposed in the optical transmission path,a demultiplexer for being supplied with the optical signal transmittedover the optical transmission path via the node and demultiplexing theoptical signal into the optical signals of respective wavelengths; andoptical receiving means for receiving the optical signals of respectivewavelengths demultiplexed by the demultiplexer; the multiplexercomprising an arrayed waveguide grating comprising a plurality of inputwaveguides for inputting signal lights having different wavelengths eachother, one or plural output waveguides for outputting signal lights, achannel waveguide array having waveguides which are successively longerwith predetermined waveguide length differences, an output slabwaveguide connecting an output end of the channel waveguide array to theoutput waveguides, and an input slab waveguide connecting an input endof the channel waveguide array to the input waveguides, and havingoptical input/output characteristics set to predetermined ratios for therespective input waveguides corresponding to the output waveguidesdepending on the differences between optical losses along respectivepaths in the output slab waveguide, level detecting means for detectinglevels of the signal lights input to the arrayed waveguide grating, andlevel adjusting means for comparing the levels of the signal lightsdetected by the level detecting means with predetermined levels for therespective wavelengths, and adjusting output levels of the signal lightsto set the levels of the waveguides multiplexed by the arrayed waveguidegrating to desired values; the demultiplexer comprising an arrayedwaveguide grating comprising one or plural input waveguides forinputting signal lights, a plurality of output waveguides for outputtingsignal lights, a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences, aninput slab waveguide connecting an input end of the channel waveguidearray to the input waveguides, and an output slab waveguide connectingan output end of the channel waveguide array to the output waveguides,and having optical input/output characteristics set to predeterminedratios for the respective output waveguides with respect to the inputwaveguides depending on the differences between optical losses alongrespective paths in the output slab waveguide, and level adjusting meansfor being supplied with the signal lights of respective wavelengths fromthe output waveguides of the arrayed waveguide grating, and adjustingoutput levels of the signal lights to desired values.

With the twenty-sixth aspect of the present invention, the opticalcommunication system, which is of a linear type, comprises opticaltransmitting means, a multiplexer for wavelength-division multiplexingthe optical signals of respective wavelengths transmitted by the lighttransmitting means, an optical transmission path for transmitting awavelength-division multiplexed optical signal output from themultiplexer, a node disposed in the optical transmission path, ademultiplexer for being supplied with the optical signal transmittedover the optical transmission path via the node and demultiplexing theoptical signal into the optical signals of respective wavelengths, andoptical receiving means for receiving the optical signals of respectivewavelengths demultiplexed by the demultiplexer. The multiplexercomprises a device according to the twentieth aspect, and thedemultiplexer comprises a device according to the eighteenth aspect,thus setting optical input/output characteristics to predeterminedratios.

According to a twenty-seventh aspect of the present invention, anoptical communication system comprises: an annular transmission pathhaving a plurality of nodes interconnected in a ring by a transmissionpath, for transmitting a multiplexed optical signal over thetransmission path; each of the nodes having a demultiplexer fordemultiplexing a multiplexed optical signal into optical signals ofrespective wavelengths, and a multiplexer for multiplexing thedemultiplexed optical signals of respective wavelengths; thedemultiplexer comprising an arrayed waveguide grating comprising one orplural input waveguides for inputting signal lights, a plurality ofoutput waveguides for outputting signal lights, a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences, an input slab waveguide connecting aninput end of the channel waveguide array to the input waveguides, and anoutput slab waveguide connecting an output end of the channel waveguidearray to the output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to the input waveguides, and level adjustingmeans for being supplied with the signal lights of respectivewavelengths from the output waveguides of the arrayed waveguide grating,and adjusting output levels of the signal lights to desired values; themultiplexer comprising an arrayed waveguide grating having a pluralityof input waveguides for inputting signal lights having differentwavelengths each other, one or plural output waveguides for outputtingsignal lights, a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences, anoutput slab waveguide connecting an output end of the channel waveguidearray to the output waveguides, and an input slab waveguide connectingan input end of the channel waveguide array to the input waveguides, andhaving optical input/output characteristics set to predetermined ratiosfor the respective input waveguides corresponding to the outputwaveguides, level detecting means for detecting levels of the signallights input to the arrayed waveguide grating, and level adjusting meansfor comparing the levels of the signal lights detected by the leveldetecting means with predetermined levels for the respectivewavelengths, and adjusting output levels of the light signals to set thelevels of the waveguides multiplexed by the arrayed waveguide grating todesired values.

With the twenty-seventh aspect of the present invention, the opticalcommunication system, which is of an annular type, comprises an annulartransmission path having a plurality of nodes interconnected in a ringby a transmission path, for transmitting a wavelength-divisionmultiplexed optical signal over the transmission path, each of the nodeshaving a demultiplexer for demultiplexing a wavelength-divisionmultiplexed optical signal into optical signals of respectivewavelengths, and a multiplexer for multiplexing the demultiplexedoptical signals of respective wavelengths. The demultiplexer comprises:a device according to the seventeenth aspect, and the demultiplexercomprises a device according to the nineteenth aspect, thus settingoptical input/output characteristics to predetermined ratios.

According to a twenty-eighth aspect of the present invention, an opticalcommunication system comprises: an annular transmission path having aplurality of nodes interconnected in a ring by a transmission path, fortransmitting a multiplexed optical signal over the transmission path;each of the nodes having a demultiplexer for demultiplexing amultiplexed optical signal into optical signals of respectivewavelengths, and a multiplexer for multiplexing the demultiplexedoptical signals of respective wavelengths; the demultiplexer comprisingan arrayed waveguide grating comprising one or plural input waveguidesfor inputting signal lights, a plurality of output waveguides foroutputting signal lights, a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences, an input slab waveguide connecting an input end of thechannel waveguide array to the input waveguides, and an output slabwaveguide connecting an output end of the channel waveguide array to theoutput waveguides, and having optical input/output characteristics setto predetermined ratios for the respective output waveguides withrespect to the input waveguides depending on the differences betweenoptical losses along respective paths in the output slab waveguide, andlevel adjusting means for being supplied with the signal lights ofrespective wavelengths from the output waveguides of the arrayedwaveguide grating, and adjusting output levels of the signal lights todesired values; the multiplexer comprising an arrayed waveguide gratingcomprising a plurality of input waveguides for inputting signal lightshaving different wavelengths each other, one or plural output waveguidesfor outputting signal lights, a channel waveguide array havingwaveguides which are successively longer with predetermined waveguidelength differences, an output slab waveguide connecting an output end ofthe channel waveguide array to the output waveguides, and an input slabwaveguide connecting an input end of the channel waveguide array to theinput waveguides, and having optical input/output characteristics set topredetermined ratios for the respective input waveguides correspondingto the output waveguides depending on the differences between opticallosses along respective paths in the output slab waveguide, leveldetecting means for detecting levels of the signal lights input to thearrayed waveguide grating, and level adjusting means for comparing thelevels of the signal lights detected by the level detecting means withpredetermined levels for the respective wavelengths, and adjustingoutput levels of the signal lights to set the levels of the waveguidesmultiplexed by the arrayed waveguide grating to desired values.

With the twenty-eighth aspect of the present invention, the opticalcommunication system, which is of an annular type, comprises an annulartransmission path having a plurality of nodes interconnected in a ringby a transmission path, for transmitting a multiplexed optical signalover the transmission path, each of the nodes having a demultiplexer fordemultiplexing a wavelength-division multiplexed optical signal intooptical signals of respective wavelengths, and a multiplexer forwavelength-division multiplexing the demultiplexed optical signals ofrespective wavelengths. The demultiplexer comprises a device accordingto the eighteenth aspect, and the demultiplexer comprises a deviceaccording to the twentieth aspect, thus setting optical input/outputcharacteristics to predetermined ratios.

According to the twenty-first through twenty-eighth aspects of thepresent invention, input/output characteristics can be changed or outputcharacteristics can be made flat without the need for attenuators,amplifiers, or signal level adjusting means outside of the waveguidedevice. Therefore, the overall system can be simplified, made highlyreliable, and reduced in cost.

According to a twenty-ninth aspect of the present invention, a waveguidedevice comprises one or plural input waveguides for inputting signallights, a plurality of output waveguides for outputting signal lights,and a slab waveguide having optical input/output characteristics set topredetermined ratios for the respective output waveguides with respectto the input waveguides.

The twenty-ninth aspect of the present invention is concerned with thedemultiplexing of light, and optical input/output characteristics areset to predetermined ratios for the respective output waveguides withrespect to the input waveguides. This makes it unnecessary to employexternal circuit parts for compensating for loss differences.

With the twenty-ninth and subsequent aspects of the present invention,unlike the twenty-eighth and former aspects of the present invention,the waveguide device does not have a channel waveguide, an input slabwaveguide, or an output waveguide as an indispensable component with thetwenty-eighth and former aspects of the present invention, the inputwaveguide is disposed on the input side of the input slab waveguide, andthe output waveguide is disposed on the output side of the output slabwaveguide. With the twenty-ninth and subsequent aspects of the presentinvention, a device present on the input side of one slab waveguide isreferred to as an input waveguide, and a device present on the outputside of the slab waveguide is referred to as an output waveguide. Theslab waveguide referred to in the twenty-ninth and subsequent aspects ofthe present invention may be regarded as an input slab waveguide of anarrayed waveguide grating or an output slab waveguide of an arrayedwaveguide grating. In other applications, e.g., in a single- ormulti-stage star coupler, one or more waveguide devices can be used incombination. The waveguide device may be used in other applications thanthe arrayed waveguide device and the star coupler.

If the slab waveguide referred to in the twenty-ninth and subsequentaspects of the present invention corresponds to an input waveguide, thenthe input waveguide is the same as the input waveguide referred to inthe twenty-eighth and former aspects of the present invention, but theoutput waveguide may correspond to individual waveguides of the channelwaveguide array as the output waveguide is the waveguide on the outputside. Similarly, if the slab waveguide referred to in the twenty-ninthand subsequent aspects of the present invention corresponds to an outputwaveguide, then the output waveguide is the same as the output waveguidereferred to in the twenty-eighth and former aspects of the presentinvention, but the input waveguide may correspond to individualwaveguides of the channel waveguide array as the input waveguide is thewaveguide on the input side.

According to a thirtieth aspect of the present invention, a waveguidedevice comprises: a plurality of output waveguides for outputting signallights; one or plural input waveguides for inputting signal lights; anda slab waveguide having optical input/output characteristics set topredetermined ratios for the respective input waveguides with respect tothe output waveguides.

Unlike the twenty-ninth aspect of the present invention, the thirtiethaspect of the present invention is concerned with the multiplexing oflights, and optical input/output characteristics are set topredetermined ratios for the respective input waveguides with respect tothe output waveguides. This makes it unnecessary to employ externalcircuit parts for compensating for loss differences.

According to a thirty-first aspect of the present invention, a waveguidedevice comprises: one or plural input waveguides for inputting signallights; a plurality of output waveguides for outputting signal lights;and a slab waveguide connecting the input waveguides to the outputwaveguides, the slab waveguide having a core layer disposed therein forpropagating light therethrough from the input waveguides to the outputwaveguides, the core layer being partly cut off in selected or all pathstherein which interconnect the input waveguides and the outputwaveguides, and a cladding layer disposed in cut regions of the corelayer and on opposite sides of the core layer, the cut regions in thepaths having cut lengths set to predetermined values in the direction inwhich the signal lights propagate, depending on optical losses of thesignal lights propagated in the paths.

With the thirty-first aspect of the present invention, the core layer ofthe slab waveguide is partly cut off as required, and the optical losseswith respect to the output waveguides at the time of demultiplexing thelight signal are adjusted based on the lengths of the cut regions.

According to a thirty-second aspect of the present invention, awaveguide device comprises: a plurality of output waveguides foroutputting signal lights; one or plural input waveguides for inputtingsignal lights; and a slab waveguide connecting the input waveguides tothe output waveguides, the slab waveguide having a core layer disposedtherein for propagating light therethrough from the input waveguides tothe output waveguides, the core layer being partly cut off in selectedor all paths therein which interconnect the input waveguides and theoutput waveguides, and a cladding layer disposed in cut regions of thecore layer and on opposite sides of the core layer, the cut regions inthe paths having cut lengths set to predetermined values in thedirection in which the signal lights propagate, depending on opticallosses of the signal lights propagated in the paths.

With the thirty-second aspect of the present invention, the core layerof the slab waveguide is partly cut off as required, and the opticallosses of the signal lights to be multiplexed into the output waveguidesat the time of demultiplexing the light signal are adjusted based on thelengths of the cut regions.

According to a thirty-third aspect of the present invention, a waveguidedevice comprises: one or plural input waveguides for inputting signallights; a slab waveguide having an input end connected to the inputwaveguides; and an output waveguide having a plurality of waveguidesconnected to an output end of the slab waveguide, wherein each ofselected or all of the waveguides have a core layer disposed therein forpropagating light therethrough, the core layer being partly cut off, anda cladding layer disposed in cut regions of the core layer and onopposite sides of the core layer, the cut regions having cut lengths setto predetermined values depending on optical losses of the signal lightspropagated in the waveguides.

With thirty-third aspect of the present invention, whereas the corelayer of the slab waveguide is partly cut off as required with thethirty-first aspect of the present invention, the core layer of some orall of the output waveguides for propagating the signal lights outputfrom the slab waveguide is partly cut off as required, and the opticallosses with respect to the output waveguides are adjusted based on thelengths of the cut regions.

According to a thirty-fourth aspect of the present invention, awaveguide device comprises: an input waveguide having a plurality ofwaveguides for inputting signal lights, wherein each of selected or allof the waveguides have a core layer disposed therein for propagatinglight therethrough, the core layer being partly cut off, and a claddinglayer disposed in cut regions of the core layer and on opposite sides ofthe core layer, the cut regions having cut lengths set to predeterminedvalues depending on optical losses of the signal lights propagated inthe waveguides; one or plural output waveguides for outputting signallights; and a slab waveguide interconnecting the input waveguides andthe output waveguides.

With the thirty-fourth aspect of the present invention, whereas the corelayer of the slab waveguide is partly cut off as required with thethirty-second aspect of the present invention, the core layer of some orall of the input waveguides for transmitting the signal lights into theslab waveguide is partly cut off as required, and the optical losseswith respect to the input waveguides are adjusted based on the lengthsof the cut regions.

According to a thirty-fifth aspect of the present invention, a waveguidedevice comprises: one or plural input waveguides for inputting signallights; a slab waveguide having an input end connected to output ends ofthe input waveguides; and an output waveguide having a plurality ofwaveguides connected to an output end of the slab waveguide, whereinselected or all of the waveguides have ends having respective centralpositions displaced from corresponding focused positions in a directionperpendicular to central axes of the waveguides by predetermined valuesdepending on losses to be given to the signal lights propagated in thewaveguides.

Usually, the focused positions located in the vicinity of the boundaryof the slab waveguide at its output end are aligned with the centralaxes of the output waveguides to increase the coupling efficiency. Withthe thirty-fifth aspect of the present invention, the central positionsof the ends of the output waveguides which face the slab waveguide aredisplaced from the corresponding focused positions in the directionperpendicular to the central axes of the output waveguides bypredetermined values depending on losses to be given to the signallights propagated in the output waveguides, thereby adjusting the lossesof the signal lights propagated in the output waveguides.

According to a thirty-sixth aspect of the present invention, a waveguidedevice comprises: a slab waveguide; an output waveguide connected to anoutput end of the slab waveguide; and a plurality of input waveguideshaving respective ends connected to an input end of the slab waveguide,wherein selected or all of the ends have respective central positionsdisplaced from corresponding focused positions in a directionperpendicular to central axes of the input waveguides by predeterminedvalues depending on losses to be given to the signal lights propagatedin the output waveguides.

Usually, a plurality of light emission points on a slab waveguide arealigned with the central axes of input waveguides are aligned toincrease the coupling efficiency. With the thirty-sixth aspect of thepresent invention, distances by which the input waveguides are displacedin the direction perpendicular to the central axes thereof from thelight emission points which are cophasal from the focused positions areset depending on losses to be given to the signal lights propagated inthe output waveguides. The losses of the signal lights propagated in theoutput waveguides are adjusted based on the distances by which the inputwaveguides are displaced.

According to a thirty-seventh aspect of the present invention, awaveguide device comprises: one or plural input waveguides for inputtingsignal lights; a slab waveguide having an input end connected to outputends of the input waveguides; and a plurality of output waveguideshaving respective ends connected to an output end of the slab waveguide,wherein selected or all of central axes of the output waveguides areinclined at the interconnected points of the output waveguides and theslab waveguides at respective angles depending on losses to be given tothe signal lights coupled at the interconnected points.

With the thirty-seventh aspect of the present invention, the anglesbetween the light emission points on the input waveguides and the slabwaveguides and the central axes of the output waveguides are setdepending on losses to be given to the signal lights, for therebyadjusting the losses of the signal lights coupled with the outputwaveguides.

According to a thirty-eighth aspect of the present invention, awaveguide device comprises: one or plural output waveguides foroutputting signal lights; a slab waveguide having an output endconnected to input ends of the output waveguides; and a plurality ofinput waveguides having respective ends connected to an input end of theslab waveguide, wherein selected or all of central axes of the inputwaveguides are inclined at the interconnected points of the inputwaveguides and the slab waveguides at respective angles depending onlosses to be given to the signal coupled at the interconnected points.

With the thirty-eighth aspect of the present invention, the anglesbetween the light emission points on the slab waveguides and the outputwaveguides and the central axes of the input waveguides are setdepending on losses to be given to the signal lights, for therebyadjusting the losses of the signal lights in the input waveguides whenthe signal lights are transmitted from the input waveguides to the slabwaveguide.

According to a thirty-ninth aspect of the present invention, a waveguidedevice comprises: one or plural input waveguides for inputting signallights; a slab waveguide having an input end connected to output ends ofthe input waveguides; and a plurality of output waveguides havingrespective ends connected to an output end of the slab waveguide,wherein selected or all of the ends have waveguide widths set to valuesdepending on losses to be given to the signal lights.

With the thirty-ninth aspect of the present invention, the widths, inthe direction perpendicular to the propagation axes, of selected or allof the output waveguides are set to values depending on losses to begiven to the signal lights, for thereby adjusting the losses of thesignal lights propagated in the output waveguides.

According to a fortieth aspect of the present invention, a waveguidedevice comprises: one or plural output waveguides for outputting signallights; a slab waveguide having an output end connected to input ends ofthe output waveguides; and a plurality of input waveguides havingrespective ends connected to an input end of the slab waveguide, whereinselected or all of the ends have waveguide widths set to valuesdepending on losses to be given to the signal lights.

With the fortieth aspect of the present invention, the widths, in thedirection perpendicular to the propagation axes, of selected or all ofthe input waveguides at their ends connected to the input slab waveguideare set to values depending on losses to be given to the signal lights,for thereby adjusting the losses of the signal lights propagated in theinput waveguides.

According to a forty-first aspect of the present invention, a waveguidedevice comprises: one or plural input waveguides for inputting signallights; a slab waveguide having an input end connected to output ends ofthe input waveguides; and a plurality of output waveguides havingrespective ends connected to an output end of the slab waveguide,wherein the lengths between the ends of the output waveguides and theinput waveguides are displaced in the direction of propagation axes ofthe output waveguides depending on losses to be given to the signallights propagated from the input waveguides to the ends of the outputwaveguides.

Usually, the focused positions located in the vicinity of the boundaryof the slab waveguide at its output end are aligned with the ends of theoutput waveguides to provide a focused state to increase the couplingefficiency to the output waveguides. With the forty-first aspect of thepresent invention, the lengths between the ends of the output waveguidesand the focused positions are displaced, for some or all of the outputwaveguides, in the direction of propagation axes of the outputwaveguides depending on losses to be given to the signal lightspropagated to the output waveguides, for thereby adjusting the losses ofthe signal lights propagated in the output waveguides.

According to a forty-second aspect of the present invention, a waveguidedevice comprises: one or plural output waveguides for outputting signallights; a slab waveguide having an output end connected to input ends ofthe output waveguides; and a plurality of input waveguides havingrespective ends connected to an input end of the slab waveguide, whereinthe lengths between the ends of the output waveguides and the inputwaveguides are displaced in the direction of propagation axes of theoutput waveguides depending on losses to be given to the signal lightspropagated from the output waveguides to the ends of the inputwaveguides.

Usually, a plurality of light emission points which are cophasal withfocused positions located in the vicinity of the boundary of the slabwaveguide at its output end are aligned with the ends of the inputwaveguides to increase the coupling efficiency of signal lights from theinput waveguides coupled to the output waveguides. With the forty-secondaspect of the present invention, some or all of the input waveguides aredisplaced from their normal positions in the direction of thepropagation axes depending on losses to be given to the signal lightspropagated in the input waveguides over the distances from the ends ofthe input waveguides to the focused positions, for thereby adjusting thelosses of the signal lights.

With the twenty-ninth through forty-second aspects of the presentinvention, since the losses of the signal lights in the respectivewaveguides in the waveguide device are different from each other,input/output characteristics can be changed or output characteristicscan be made flat without the need for attenuators, amplifiers, or signallevel adjusting means outside of the waveguide device. Therefore, amodule or a device using an arrayed waveguide grating can be simplified,made highly reliable, and reduced in cost.

According to a forty-third aspect of the present invention, ademultiplexer comprises: a waveguide device having one or plural inputwaveguides for inputting signal lights, a plurality of output waveguidesfor outputting signal lights, and a slab waveguide having opticalinput/output characteristics set to predetermined ratios for therespective output waveguides with respect to the input waveguides; andlevel adjusting means for being supplied with signal lights output fromthe output waveguides of the waveguide device, and adjusting outputlevels of the signal lights to desired values.

With the forty-third aspect of the present invention, the waveguidedevice itself sets the optical input/output characteristics topredetermined ratios for the respective output waveguides with respectto the input waveguides depending on optical loss differences at theboundary of the slab waveguide, and the level adjusting means issupplied with the signal lights of respective wavelengths from theoutput waveguides and adjusts output levels of the signal lights todesired values. The input/output characteristics can thus be made flator freely adjusted. Furthermore, since the demultiplexer comprises thewaveguide device with the input/output characteristics adjusted and thelevel adjusting means for adjusting the output levels of the wavelengthsoutput from the output waveguides, errors of the input/outputcharacteristics of the waveguide device itself can be corrected.

According to a forty-fourth aspect of the present invention, amultiplexer comprises: a plurality of light sources for respectivesignals; a waveguide device having a plurality of input waveguides forinputting signal lights, one or plural output waveguides for outputtingsignal lights, and a slab waveguide having optical input/outputcharacteristics set to predetermined ratios for the respective inputwaveguides with respect to the output waveguides; level detecting meansfor detecting levels of the signal lights input from the light sourcesto the waveguide device, and level adjusting means for comparing thelevels of the signal lights detected by the level detecting means withpredetermined levels for the respective signal lights; and adjustingoutput levels of the respective signal lights to set the levels of thesignal lights multiplexed by the waveguide device to desired values.

With the forty-fourth aspect of the present invention, the waveguidedevice itself sets the optical input/output characteristics topredetermined ratios for the respective input waveguides with respect tothe output waveguides depending on optical loss differences at theboundary of the slab waveguide, and the levels of the signal lightsinput from the light sources to the waveguide device are detected by thelevel detecting means. By adjusting the output levels of the lightsources, the levels of the signal lights of the respective wavelengthswhich have been multiplexed by the waveguide device are set to desiredvalues. The input/output characteristics can thus be made flat or freelyadjusted at the output waveguides. Furthermore, errors of theinput/output characteristics of the waveguide device itself can becorrected.

According to a forty-fifth aspect of the present invention, an opticalcommunication system comprises: optical transmitting means fortransmitting optical signals of respective wavelengths parallel to eachother; a multiplexer for multiplexing the optical signals of respectivewavelengths transmitted by the light transmitting means; an opticaltransmission path for transmitting a multiplexed optical signal outputfrom the multiplexer; a node disposed in the optical transmission pathand having a waveguide device; a demultiplexer for being supplied withthe optical signal transmitted over the optical transmission path viathe node and demultiplexing the optical signal into the optical signalsof respective wavelengths; and optical receiving means for receiving theoptical signals of respective wavelengths demultiplexed by thedemultiplexer; the multiplexer comprising a plurality of inputwaveguides for inputting signal lights, one or plural output waveguidesfor outputting signal lights, and a slab waveguide having opticalinput/output characteristics set to predetermined ratios for therespective input waveguides with respect to the output waveguides; thedemultiplexer comprising a waveguide device comprising one or pluralinput waveguides for inputting signal lights, a plurality of outputwaveguides for outputting signal lights, and a slab waveguide havingoptical input/output characteristics set to predetermined ratios for therespective output waveguides with respect to the input waveguides.

With the forty-fifth aspect of the present invention, the opticalcommunication system, which is of a linear type, comprises opticaltransmitting means, a multiplexer for wavelength-division multiplexingthe optical signals of respective wavelengths transmitted by the lighttransmitting means, an optical transmission path for transmitting awavelength-division multiplexed optical signal output from themultiplexer, a node disposed in the optical transmission path and havinga waveguide device, a demultiplexer for being supplied with the opticalsignal transmitted over the optical transmission path via the node anddemultiplexing the optical signal into the optical signals of respectivewavelengths, and optical receiving means for receiving the opticalsignals of respective wavelengths demultiplexed by the demultiplexer.The multiplexer comprises a waveguide device according to the thirtiethaspect and sets optical input/output characteristics to predeterminedratios for the respective input waveguides with respect to the outputwaveguides that are connected to the output end of the slab waveguide.The demultiplexer comprises a waveguide device according to thetwenty-ninth aspect and sets optical input/output characteristics topredetermined ratios for the respective output waveguides with respectto the input waveguides.

According to a forty-sixth aspect of the present invention, an opticalcommunication system comprises: an annular transmission path having aplurality of nodes interconnected in a ring by a transmission path, fortransmitting a multiplexed optical signal over the transmission path;each of the nodes having a first waveguide device for demultiplexing amultiplexed optical signal into optical signals of respectivewavelengths; and a second waveguide device for multiplexing thedemultiplexed optical signals of respective wavelengths, the firstwaveguide device comprising one or plural input waveguides forinputting, signal lights, a plurality output waveguides for outputtingsignal lights, and a slab waveguide having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to the input waveguides, the second waveguidedevice comprising a plurality of input waveguides for inputting signallights, one or plural output waveguides for outputting signal lights,and a slab waveguide having optical input/output characteristics set topredetermined ratios for the respective input waveguides with respect tothe output waveguides.

With the forty-sixth aspect of the present invention, the opticalcommunication system, which is of an annular type, comprises an annulartransmission path having a plurality of nodes interconnected in a ringby a transmission path, for transmitting a multiplexed optical signalover the transmission path, each of the nodes having a first waveguidedevice for demultiplexing a multiplexed optical signal into opticalsignals of respective wavelengths, and a second waveguide device forwavelength-division multiplexing the demultiplexed optical signals ofrespective wavelengths. The first waveguide device comprises a waveguidedevice according to the thirtieth aspect and sets optical input/outputcharacteristics to predetermined ratios for the respective inputwaveguides with respect to the output waveguides that are connected tothe output end of the slab waveguide. The second waveguide devicecomprises a waveguide device according to the twenty-ninth aspect andsets optical input/output characteristics to predetermined ratios forthe respective output waveguides with respect to the input waveguides.

According to a forty-seventh aspect of the present invention, an opticalcommunication system comprises: optical transmitting means fortransmitting optical signals of respective wavelengths parallel to eachother; a multiplexer for multiplexing the optical signals of respectivewavelengths transmitted by the light transmitting means; an opticaltransmission path for transmitting a multiplexed optical signal outputfrom the multiplexer; a node disposed in the optical transmission path;a demultiplexer for being supplied with the optical signal transmittedover the optical transmission path via the node and demultiplexing theoptical signal into the optical signals of respective wavelengths; andoptical receiving means for receiving the optical signals of respectivewavelengths demultiplexed by the demultiplexer; the multiplexercomprising a plurality of light sources for respective signals, awaveguide device having a plurality of input waveguides for inputtingsignal lights, one or plural output waveguides for outputting signallights, and a slab waveguide having optical input/output characteristicsset to predetermined ratios for the respective input waveguides withrespect to the output waveguides, level detecting means for detectinglevels of the signal lights input from the light sources to thewaveguide device, and level adjusting means for comparing the levels ofthe signal lights detected by the level detecting means withpredetermined levels for the respective signal lights, and adjustingoutput levels of the respective signal lights to set the levels of thesignal lights multiplexed by the waveguide device to desired values; thedemultiplexer comprising a waveguide device having one or plural inputwaveguides for inputting signal lights, a plurality of output waveguidesfor outputting signal lights, and a slab waveguide having opticalinput/output characteristics set to predetermined ratios for therespective output waveguides with respect to the input waveguides, andlevel adjusting means for being supplied with the signal lights from theoutput waveguides of the waveguide device, and adjusting output levelsof the signal lights to desired values.

With the forty-seventh aspect of the present invention, the opticalcommunication system, which is of a linear type, comprises: opticaltransmitting means, a multiplexer for wavelength-division multiplexingthe optical signals of respective wavelengths transmitted by the lighttransmitting means; an optical transmission path for transmitting awavelength-deivision multiplexed optical signal output from themultiplexer; a node disposed in the optical transmission path, ademultiplexer for being supplied with the optical signal transmittedover the optical transmission path via the node and demultiplexing theoptical signal into the optical signals of respective wavelengths; andoptical receiving means for receiving the optical signals of respectivewavelengths demultiplexed by the demultiplexer. The multiplexercomprises a device according to the forty-fourth aspect, and thedemultiplexer comprises a device according to the forty-third aspect,setting optical input/output characteristics to predetermined ratios.

According to a forty-eighth aspect of the present invention, an opticalcommunication system comprises: an annular transmission path having aplurality of nodes interconnected in a ring by a transmission path, fortransmitting a multiplexed optical signal over the transmission path;each of the nodes having a demultiplexer for demultiplexing amultiplexed optical signal into optical signals of respectivewavelengths, and a multiplexer for multiplexing the demultiplexedoptical signals of respective wavelengths; the demultiplexer comprisinga waveguide device having one or-plural input waveguides for inputtingsignal lights, a plurality of output waveguides for outputting signallights, and a slab waveguide having optical input/output characteristicsset to predetermined ratios for the respective output waveguides withrespect to the input waveguides, and level adjusting means for beingsupplied with the signal lights from the output waveguides of thewaveguide device, and adjusting output levels of the signal lights todesired values; and the multiplexer comprising a plurality of lightsources for respective signals, a waveguide device having a plurality ofinput waveguides for inputting signal lights, one or plural outputwaveguides for outputting signal lights, and a slab waveguide havingoptical input/output characteristics set to predetermined ratios for therespective input waveguides with respect to the output waveguides, leveldetecting means for detecting levels of the signal lights input from thelight sources to the waveguide device, and level adjusting means forcomparing the levels of the signal lights detected by the leveldetecting means with predetermined levels for the respective signallights, and adjusting output levels of the respective signal lights toset the levels of the signal lights multiplexed by the waveguide deviceto desired values.

With the forty-eighth aspect of the present invention, the opticalcommunication system, which is of an annular type, comprises an annulartransmission path having a plurality of nodes interconnected in a ringby a transmission path, for transmitting a wavelength-devisionmultiplexed optical signal over the transmission path, each of the nodeshaving a demultiplexer for demultiplexing a multiplexed optical signalinto optical signals of respective wavelengths, and a multiplexer formultiplexing the demultiplexed optical signals of respectivewavelengths. The demultiplexer comprises a device according to theforty-third aspect, and the multiplexer comprises a device according tothe forty-fourth aspect, setting optical input/output characteristics topredetermined ratios.

According to the forty-fifth through forty-eighth aspects of the presentinvention, input/output characteristics can be changed or outputcharacteristics can be made flat without the need for attenuators,amplifiers, or signal level adjusting means outside of the waveguidedevice. Therefore, the overall system can be simplified, made highlyreliable, and reduced in cost.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an overall arrangement of a conventionalarrayed waveguide grating;

FIG. 2 is a plan view of an overall arrangement of a slab waveguide ofan arrayed waveguide grating according to a first embodiment of thepresent invention;

FIG. 3 is an enlarged fragmentary plan view of a portion of the outputend of the slab waveguide according to the first embodiment;

FIG. 4 is a cross-sectional view of the slab waveguide taken along anoptical path leading to a compensation output waveguide positioned in arelatively peripheral region of the slab waveguide according to thefirst embodiment;

FIG. 5 is a cross-sectional view of the slab waveguide taken along anoptical path leading to a compensation output waveguide positioned in arelatively central region of the slab waveguide according to the firstembodiment;

FIG. 6 is a diagram showing the relationship between the cut length of acore layer and an increase in an optical loss caused by the cutting ofthe core layer in the slab waveguide according to the first embodiment;

FIG. 7 is an enlarged fragmentary plan view of a peripheral region ofthe output end of a slab waveguide of an arrayed waveguide gratingaccording to a second embodiment of the present invention;

FIG. 8 is a view illustrative of how light is propagated in acompensation output waveguide, which does not perform outputcompensation, positioned in a relatively peripheral region of the slabwaveguide according to the second embodiment;

FIG. 9 is a view illustrative of how light is propagated in acompensation output waveguide, which performs slight output compensationas compared with the compensation output waveguide shown in FIG. 8, ofthe slab waveguide according to the second embodiment;

FIG. 10 is a diagram showing the relationship between the axialmisalignment of each output port and a loss caused thereby in the slabwaveguide according to the second embodiment;

FIG. 11 is an enlarged fragmentary plan view of a portion of a slabwaveguide of an arrayed waveguide grating according to a thirdembodiment of the present invention;

FIG. 12 is an enlarged fragmentary plan view showing the relationshipbetween optical paths leading to respective output ports and the centralaxes of compensation output waveguides in slab waveguide according tothe third embodiment;

FIG. 13 is a diagram showing the relationship between the angle of thecentral axis and a loss caused thereby in the slab waveguide accordingto the third embodiment;

FIG. 14 is an enlarged fragmentary plan view of a peripheral region ofthe output end of a slab waveguide of an arrayed waveguide gratingaccording to a fourth embodiment of the present invention;

FIG. 15 is a diagram showing the relationship between the ratio betweenthe spot size of a focused spot and the spot size in a waveguide mode ofthe waveguide, and a loss caused thereby in the slab waveguide accordingto the fourth embodiment;

FIG. 16 is an enlarged fragmentary plan view of a portion of a slabwaveguide of an arrayed waveguide grating according to a fifthembodiment of the present invention;

FIG. 17 is a view showing, in principle, optical losses caused by aprojecting portion of the output end of the slab waveguide according tothe fifth embodiment;

FIG. 18 is a diagram showing the relationship between a shifted focusdistance F and a loss caused thereby in the slab waveguide according tothe fifth embodiment;

FIG. 19 is a view showing the manner in which optical signals can bemultiplexed and demultiplexed using the arrayed waveguide gratingaccording to the first embodiment;

FIG. 20 is a block diagram of a demultiplexer according to a sixthembodiment of the present invention;

FIG. 21 is a block diagram of a multiplexer according to a seventhembodiment of the present invention;

FIG. 22 is a block diagram of an optical communication system accordingto an eighth embodiment of the present invention;

FIG. 23 is a block diagram of a node of the optical communication systemaccording to the eighth embodiment; and

FIG. 24 is a diagram showing, in principle, of the concept of a focalpoint according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1st Embodiment

FIG. 2 shows in plan an output slab waveguide of an arrayed waveguidegrating according to a first embodiment of the present invention. Thearrayed waveguide grating according to the first embodiment has astructure which is basically the same as the conventional arrayedwaveguide grating shown in FIG. 1. As shown in FIG. 2, the output slabwaveguide, denoted by 101, has an input end connected to channelwaveguide array 102 which sends light into output slab waveguide 101.Output waveguides 105 have waveguides 104, which correspond to outputwaveguides 14 shown in FIG. 1, having respectively ends connected to theoutput end of output slab waveguide 101 at a position opposite to theposition where channel waveguide array 102 is connected to output slabwaveguide 101. Light that has entered from channel waveguide array 102into output slab waveguide 101 is propagated through output waveguide105.

FIG. 3 shows in enlarged fragmentary plan a portion of the output end ofoutput slab waveguide 101. Waveguides 104 of output waveguides 105 aredivided into compensation waveguides 104 _(m) through 104 _(m+n) withthe intensity of incoming light being compensated for andnon-compensation waveguides 104 _(k) through 104 _(k+n) with theintensity of incoming light being not compensated for. Compensationwaveguides 104 _(m) through 104 _(m+n) are designed to have opticalsignal levels compensated for, and can be used as monitoring waveguides.Non-compensation waveguides 104 _(k) through 104 _(k+m) are generallyused in applications where a reduction in optical signal levels due tocompensation is not desirable. All waveguides 104 of output waveguides105 may be compensation waveguides.

Channel waveguide array 102 has core layer 111 for transmitting lightentered from channel waveguide array 102. Core layer 111 is disposed inoutput slab waveguide 101 and extends to the position where outputwaveguides 105 are connected to output slab waveguide 101. As shown inFIG. 4, channel waveguide array 102 also has cladding layer 112vertically (in the direction normal to the sheets of FIGS. 2 and 3)sandwiching core layer 111 for thereby confining light in core layer111. According to the first embodiment, the portion of core layer 111which corresponds to waveguides 104 _(m) through 104 _(m+n) is cut offin optical paths 113, providing a recess which is filled with claddinglayer 112.

FIGS. 4 and 5 show core layer 111 in cross section taken along tworespective optical paths illustrated in FIG. 3. Specifically, thecross-sectional views in FIGS. 4 and 5 of output slab waveguide 101 aretaken respectively along optical path 113 _(m+n) and optical path 113_(m+1) in the direction normal to the sheets of FIGS. 4 and 5. If corelayer 111 were not cut off, the intensity of light emitted from channelwaveguide array 102 shown in FIG. 2 and propagating along optical path113 _(m+n) leading to compensation waveguide 104 _(m+n) shown in FIG. 4would be greater than the intensity of light emitted from channelwaveguide array 102 shown in FIG. 2 and propagating along optical path113 _(m+1) leading to compensation waveguide 104 _(m+1) shown in FIG. 5.These different intensities of light are equalized by adjusting thelengths L_(m+n), L_(m+1) by which core layer 111 is cut off respectivelyalong optical paths 113 _(m+n), 113 _(m+1).

Specifically, the cut length L_(m+n) along optical path 113 _(m+n) shownin FIG. 4 is relatively short, and a substantial portion of lightemitted from a cut end of input core layer 111 _(IN) couple to outputcore layer 111 _(OUT) and reaches compensation waveguide 104 _(m+n).However, the cut length L_(m+1) along optical path 113 _(m+1) shown inFIG. 5 is relatively large, and a substantial portion of light emittedfrom the cut end of input core layer 111 _(IN) does not couple to outputcore layer 111 _(OUT). Therefore, the intensity of light that reachescompensation waveguide 104 _(m+1) is greatly reduced.

The intensities of light in respective compensation waveguides 104 _(m)through 104 _(m+n) which are achieved if the core layer 111 is not cutoff are measured or theoretically determined, and the optical paths 113are partly cut off by lengths that are experimentally or theoreticallydetermined in order to equalize the different intensities of light inrespective compensation waveguides 104 _(m) through 104 _(m+n). Corelayer 111 may be cut off in desired regions by wet etching or dryetching. And the emission light from input core layer 111 _(IN) may becoupled with compensation waveguide 104 _(m) through 104 _(m+n) directlyto avoid in optical characteristics except optical loss characteristicchange.

FIG. 6 shows the relationship between the cut length of a core layer andan increase in an optical loss caused by the cutting of the core layerin the slab waveguide according to the first embodiment. It can be seenfrom FIG. 6 that as the region cut in core layer 111 is longer, the lossof light reaching waveguides 104 is greater, attenuating light reachingwaveguides 104. Some arrayed waveguide gratings, or multiplexers ordemultiplexers or optical communication systems which use arrayedwaveguide gratings may not be required to have flat signalcharacteristics. For example, if amplifiers, not shown, connected to theoutput ends of compensation waveguides 104 _(m) through 104 _(m+n) donot have flat output characteristics, then it is necessary to designtotal output characteristics in view of the output characteristics ofthe amplifiers. Actually, therefore, the intensities of optical signalsobtained by compensation waveguides 104 _(m) through 104 _(m+n) arecompensated for according to the output characteristics that are needed.

2nd Embodiment

FIG. 7 shows in enlarged fragmentary plan a peripheral region of theoutput end of a slab waveguide of an arrayed waveguide grating accordingto a second embodiment of the present invention. The arrayed waveguidegrating according to the second embodiment has a structure which isbasically the same as the conventional arrayed waveguide grating shownin FIG. 1. As shown in FIG. 7, output slab waveguide 131 has an inputend connected to channel waveguide array 102 which sends light intooutput slab waveguide 131. Optical signals that has propagated throughoutput slab waveguide 131 are brought into phase with each other andfocused at respective output port focusing positions P_(m+n), P_(m+n−1),P_(m+n−2), . . . . The optical signals that have been focused atrespective output port focusing positions P_(m+n), P_(m+n−1), P_(m+n−2),. . . are then propagated through respective compensation waveguides 132_(m+n), 132 _(m+n−1), 132 _(m+n−2), . . . serving as channel waveguideswhich correspond to output waveguides 104 shown in FIG. 1.

The arrayed waveguide grating shown in FIG. 7 differs from the arrayedwaveguide grating shown in FIG. 1 in that the core layer, not shown, ofoutput slab waveguide 131 is not cut off in optical paths, and theextensions of the central axes of some or all of compensation waveguides132 _(m+n), 132 _(m+n−1), 132 _(m+n−2), . . . are not aligned, i.e., areout of axial alignment, with corresponding output waveguide focusingpositions P_(m+n), P_(m+n−1), P_(m+n−2), . . . . In the presentembodiment, the axial misalignments are shown exaggerated for ease ofunderstanding.

FIGS. 8 and 9 are illustrative of how light is propagated in acompensation output waveguide, which does not perform outputcompensation, positioned in a relatively peripheral region of the slabwaveguide according to the second embodiment and in a compensationoutput waveguide, which performs slight output compensation, of the slabwaveguide according to the second embodiment. Compensation waveguides132 _(m+n) shown in FIG. 8 does not perform output compensation forattenuating the light. In FIG. 8, the extension of central axis 141_(m+n) of compensation waveguide 132 _(m+n) is in alignment, i.e., isnot axially misaligned, with output waveguide focusing position P_(m+n)in exactly the same manner as with the positional relationship betweeneach input port of the ordinary output slab waveguide and the channelwaveguide array. In the arrangement shown in FIG. 8, the light having aGaussian intensity distribution which has been focused at outputwaveguide focusing position P_(m+n) well matches compensation waveguide132 _(m+n) and is propagated therethrough to its output end as indicatedby arrow 142.

Compensation waveguide 132 _(m+n−1) shown in FIG. 9, which is positionedadjacent to compensation waveguide 132 _(m+n), has its central axis 141_(m+n−1), displaced from corresponding output waveguide focusingposition P_(m+n−1) by slight distance d_(m+n−1). Because of the axialmisalignment, the light having a Gaussian intensity distribution whichhas been focused at output waveguide focusing position P_(m+n−1)mismatches compensation waveguide 132 _(m+n−1) when it is propagatedtherethrough, causing a light intensity loss (attenuation). As a result,even if the intensity of light focused at output waveguide focusingposition P_(m+n−1) is greater than the intensity of light focused atoutput waveguide focusing position P_(m+n), the axial misalignment maybe set to a suitable value to equalize the intensity of light propagatedthrough compensation waveguide 132 _(m+n−1) to the intensity of lightpropagated through compensation waveguide 132 _(m+n). In this fashion,the intensities of light that are propagated through all compensationwaveguides 132 _(m+n), 132 _(m+n−1), 132 _(m+n−2), . . . can beequalized, thus providing flat output characteristics.

FIG. 10 shows the relationship between the axial misalignment of eachoutput port and a loss caused thereby in the slab waveguide according tothe second embodiment in order to obtain such flat outputcharacteristics. As with the first embodiment, the second embodimentdoes not need to be limited to obtaining flat characteristics at theoutput end. Specifically, some arrayed waveguide gratings, ormultiplexers or demultiplexers or optical communication systems whichuse arrayed waveguide gratings may not be required to have flat signalcharacteristics. For example, if amplifiers, not shown, connected to thefinal output ends, not shown, (output ends of output waveguides 14 shownin FIG. 1) from compensation waveguides 132 _(m+n), 132 _(m+n−1), 132_(m+n−2), . . . do not have flat output characteristics, then it isnecessary to design total output characteristics in view of the outputcharacteristics of the amplifiers. Actually, therefore, the intensitiesof optical signals obtained by compensation waveguides 132 _(m+n), 132_(m+n−1), 132 _(m+n−2), . . . are compensated for according to theoutput characteristics that are needed.

3rd Embodiment

FIG. 11 shows in enlarged fragmentary plan a portion of a slab waveguideof an arrayed waveguide grating according to a third embodiment of thepresent invention. The arrayed waveguide grating according to the thirdembodiment has a structure which is basically the same as theconventional arrayed waveguide grating shown in FIG. 1. As shown in FIG.11, output slab waveguide 161 is arranged to cause optical signals thathas entered from channel waveguide array 102 to be brought into phasewith each other and focused at respective output waveguide focusingpositions P_(m+n), P_(m+n−1), P_(m+n−2), . . . . The arrayed waveguidegrating has compensation waveguides 162 _(m+n), 162 _(m+n−1), 162_(m+n−2), . . . serving as output waveguides, not shown, are disposed inassociation with respective output waveguide focusing positions P_(m+n),P_(m+n−1), P_(m+n−2), . . . . Unlike the second embodiment, theextensions of the central axes of compensation waveguides 162 _(m+n),162 _(m+n−1), 162 _(m+n−2), . . . are not misaligned with respectiveoutput waveguide focusing positions P_(m+n), P_(m+n−1), P_(m+n−2), . . .. Instead, with the arrayed waveguide grating according to the thirdembodiment, the angles between optical paths 163 _(m+n), 163 _(m+n−1),163 _(m+n−2), . . . extending from the light emission points of channelwaveguide array 102 to respective output waveguide focusing positionsP_(m+n), P_(m+n−1), P_(m+n−2), . . . and corresponding compensationwaveguides 162 _(m+n), 162 _(m+n−1), 162 _(m+n−2), . . . are differentdepending on the amount by which the light is compensated for.

FIG. 12 shows in enlarged fragmentary plan the relationship betweenoptical paths leading to respective output ports and the central axes ofcompensation output waveguides in slab waveguide according to the thirdembodiment. As with the first and second embodiments, compensationwaveguide 162 _(m+n) which is positioned in a relatively peripheralregion of the output end of output slab waveguide 161 is designed tocause no light intensity loss, and the light intensity loss is increasedsuccessively from compensation waveguides 162 _(m+n), 162 _(m+n−2), . .. toward the central region. Optical path 163 _(m+n) connecting thechannel waveguide array to output waveguide focusing position P_(m+n)and central axis 165 _(m+n) of compensation waveguide 162 _(m+n) form anangle θ_(m+n) of 0° therebetween. Thus, optical path 163 _(m+n) andcentral axis 165 _(m+n) are aligned with each other, so that the lighthaving a Gaussian intensity distribution which has been focused atoutput waveguide focusing position P_(m+n) well matches compensationwaveguide 162 _(m+n) and is propagated therethrough to its output endwith the best total coupling efficiency.

Compensation waveguide 162 _(m+n−1) which is positioned adjacent tocompensation waveguide 162 _(m+n) has its central axis 165 _(m+n−1)extending out of alignment with corresponding optical path 163 _(m+n−1),but crossing corresponding optical path 163 _(m+n−1) at a relativelysmall angle θ_(m+n−1). Therefore, the light which has been focused atoutput waveguide focusing position P_(m+n−1) adjacent to outputwaveguide focusing position P_(m+n) mismatches compensation waveguide162 _(m+n−1) when it is propagated therethrough, causing a slightreduction in the total efficiency. As a result, even if the intensity oflight focused at output waveguide focusing position P_(m+n−1) is greaterthan the intensity of light focused at output waveguide focusingposition P_(m+n), the angle θ_(m+n−1) may be set to a suitable value toequalize the intensity of light propagated through the output waveguide,i.e., compensation waveguide 162 _(m+n−1) to the intensity of lightpropagated through compensation waveguide 162 _(m+n).

The angle θ_(m+n−2) between central axis 165 _(m+n−2) of compensationwaveguide 162 _(m+n−2) which is positioned adjacent to compensationwaveguide 162 _(m+n−1) toward the center and corresponding optical path163 _(m+n−2) is greater than the angle θ_(m+n−1) by a certain value.Thus, the coupling efficiency between output waveguide focusing positionP_(m+n−2) and compensation waveguide 162 _(m+n−2) is further reducedfrom the coupling efficiency between output waveguide focusing positionP_(m+n−1) and compensation waveguide 162 _(m+n−1). The intensity oflight propagated through compensation waveguide 162 _(m+n−2) can beequalized to the intensity of light propagated through compensationwaveguide 162 _(m+n−1) by setting the angle θ_(m+n−2) to a suitablevalue. In this manner, the intensities of light that are propagatedthrough all compensation waveguides 162 _(m+n), 162 _(m+n−1), 162_(m+n−2), . . . can be equalized, thus providing flat outputcharacteristics.

FIG. 13 shows the relationship between the angle of the central axis anda loss caused thereby in the slab waveguide according to the thirdembodiment. As with the first and second embodiments, the thirdembodiment does not need to be limited to obtaining flat characteristicsat the output end. Specifically, some arrayed waveguide gratings, ormultiplexers or demultiplexers or optical communication systems whichuse arrayed waveguide gratings may not be required to have flat signalcharacteristics. For example, if amplifiers, not shown, connected to thefinal output ends, not shown, (output ends of output waveguides 14 shownin FIG. 1) from compensation waveguides 162 _(m+n), 162 _(m+n−1), 162_(m+n−2), . . . do not have flat output characteristics, then it isnecessary to design total output characteristics in view of the outputcharacteristics of the amplifiers. Actually, therefore, the intensitiesof optical signals obtained by compensation waveguides 162 _(m+n), 162_(m+n−1), 162 _(m+n−2), . . . are compensated for according to theoutput characteristics that are needed.

4th Embodiment

FIG. 14 shows in enlarged fragmentary plan a peripheral region of theoutput end of a slab waveguide of an arrayed waveguide grating accordingto a fourth embodiment of the present invention. The arrayed waveguide 5grating according to the fourth embodiment has a structure which isbasically the same as the conventional arrayed waveguide grating shownin FIG. 1. As shown in FIG. 14, as with output slab waveguide 101 shownin FIG. 1, output slab waveguide 191 is arranged to cause opticalsignals that has entered from a channel waveguide array, not shown, tobe brought into phase with each other and focused at respective outputwaveguide focusing positions P_(m+a), P_(m+a−1), P_(m+a−2), . . . . Theoptical signals that have been focused at respective output waveguidefocusing positions P_(m+a), P_(m+a−1), P_(m+a−2), . . . are propagatedthrough respective compensation waveguides 192 _(m+a), 192 _(m+a−1), 192_(m+a−2), . . . .

As with the third embodiment, output waveguide focusing positionsP_(m+a), P_(m+a−1), P_(m+a−2), . . . are positioned respectively on theextensions of the central axes of corresponding compensation waveguides192 _(m+a), 192 _(m+a−1), 192 _(m+a−2), . . . . Optical paths 193_(m+a), 193 _(m+a−1), 193 _(m+a−2), . . . extending from light emissionpoints, not shown, on the channel waveguide array to respective outputwaveguide focusing positions P_(m+a), P_(m+a−1), P_(m+a−2), . . . arealigned with the central axis of corresponding compensation waveguides192 _(m+a), 192 _(m+a−1), 192 _(m+a−2), . . . . With the arrayedwaveguide grating according to the fourth embodiment, waveguide widthsW_(m+a), W_(m+a−1), W_(m+a−2), . . . of respective compensationwaveguides 192 _(m+a), 192 _(m+a−1), 192 _(m+a−2), . . . at their endsconnected to output slab waveguide 191 are different depending on theamount by which the light is compensated for.

Specifically, the amount by which the light is compensated for isadjusted based on the spot sizes of focused spots at respective outputwaveguide focusing positions P_(m+a), P_(m+a−1), P_(m+a−2), . . . andwaveguide widths W_(m+a), W_(m+a−1), W_(m+a−2), . . . of correspondingcompensation waveguides 192 _(m+a), 192 _(m+a−1), 192 _(m+a−2), . . . .

FIG. 15 shows the relationship between the ratio between the spot sizeof a focused spot and the spot size in a waveguide mode of thewaveguide, and a coupling loss caused thereby in the slab waveguideaccording to the fourth embodiment. It can be seen from FIG. 15 that thecoupling loss is greater as the ratio between the spot size of a focusedspot and the spot size in a waveguide mode of the waveguide differs morefrom 1. Since the spot size of the focused spot is constant and the spotside in the waveguide mode varies when the waveguide width varies,waveguide widths W_(m+a), W_(m+a−1), W_(m+a−2), . . . of correspondingcompensation waveguides 192 _(m+a), 192 _(m+a−1), 192 _(m+a−2), . . .are set to adjust the spot sizes of focused spots and the spot sizes inthe waveguide mode of the waveguides. In this manner, waveguide widthsW_(m+a), W_(m+a−1), W_(m+a−2), . . . of corresponding compensationwaveguides 192 _(m+a), 192 _(m+a−1), 192 _(m+a−2), . . . are set tosuitable values to set the intensities of optical signals propagatedthrough compensation waveguides (output waveguides) 192 _(m+a), 192_(m+a−1), 192 _(m+a−2), . . . to desired characteristics such as flatcharacteristics.

5th Embodiment

FIG. 16 shows in enlarged fragmentary plan a portion of a slab waveguideof an arrayed waveguide grating according to a fifth embodiment of thepresent invention. The arrayed waveguide grating according to the fifthembodiment has a structure which is basically the same as theconventional arrayed waveguide grating shown in FIG. 1. As shown in FIG.16, output slab waveguide 221 according to the fifth embodiment has anoutput end partially projecting toward output waveguides from cophasalcurve (a curve interconnecting output waveguide focusing positionsP_(m+n), P_(m+n−1), P_(m+n−2), . . . or output waveguide focusingpositions P_(m+a), P_(m+a−1), P_(m+a−2), . . . in the previousembodiment) 223 which interconnects the connected ends ofnon-compensation waveguides 222 _(k) through 222 _(k+n), andcompensation waveguides 225 _(m) through 225 _(m+n) with lightintensities compensated for are connected to the projecting portion ofthe output end. Specifically, the boundary between output slab waveguide221 and compensation waveguides 225 _(m) through 225 _(m+n) partiallyprojects from cophasal curve 223 toward the output waveguides. Insteadof projecting from cophasal curve 223 toward the output waveguides, theoutput end of output slab waveguide 221 may be retracted toward theinput end thereof.

FIG. 17 shows, in principle, optical losses caused by such a projectingportion of the output end of the slab waveguide according to the fifthembodiment. Light which has propagated through optical path 224 _(m+n)that interconnects the channel waveguide array, not shown, and outputwaveguide focusing position P_(m+n) well matches compensation waveguide225 _(m+n) disposed at output waveguide focusing position P_(m+n), andis propagated therethrough to the output end thereof. At this time, theintensity level of the light is not compensated for.

Light which has propagated through optical path 224 _(m+n−1) thatinterconnects the channel waveguide array and output waveguide focusingposition P_(m+n−1) is focused at output waveguide focusing positionP_(m+n−1), but compensation waveguide 225 _(m+n−1) is retracted by agiven length (hereinafter referred to as “shifted focus distance”)F_(m+n−1) in the direction in which the light is output. Therefore, thelight having a Gaussian intensity distribution at output waveguidefocusing position P_(m+n−1) is slightly distorted and propagated with anenlarged spot size through compensation waveguide 225 _(m+n−1), causinga coupling loss due to a mismatch. Thus, by setting the shifted focusdistance F_(m+n−1) to a suitable value, it is possible to generate acoupling loss to cancel an increase in the light intensity caused atoutput waveguide focusing position P_(m+n−1) as compared with outputwaveguide focusing position P_(m+n), thereby adjusting the intensitylevel of light propagated through compensation waveguide 225 _(m+n−1) tothe same intensity level of light propagated through compensationwaveguide 225 _(m+n).

Compensation waveguide 225 _(m+n−2) which is positioned adjacent tocompensation waveguide 225 _(m+n−1) toward the center is furtherretracted from corresponding output waveguide focusing positionP_(m+n−2) toward the output waveguide by a greater shifted focusdistance F_(m+n−2). Therefore, the coupling efficiency between outputwaveguide focusing position P_(m+n−2) and compensation waveguide 225_(m+n−2) is further reduced from the coupling efficiency between outputwaveguide focusing position P_(m+n−1) and compensation waveguide 225_(m+n−1). The intensity of light propagated through compensationwaveguide 225 _(m+n−2) can be equalized to the intensity of lightpropagated through compensation waveguide 225 _(m+n−1) by setting theshifted focus distance F_(m+n−2) to a suitable value. In this manner,the intensities of light propagated through all compensation waveguides225 _(m+n), 225 _(m+n−1), 225 _(m+n−2), . . . can be equalized, thusproviding flat output characteristics.

FIG. 18 shows the relationship between a shifted focus distance F and aloss caused thereby in the slab waveguide according to the fifthembodiment. As with the previous embodiments, the fifth embodiment doesnot need to be limited to obtaining flat characteristics at the outputend. Specifically, some arrayed waveguide gratings, or multiplexers ordemultiplexers or optical communication systems which use arrayedwaveguide gratings may not be required to have flat signalcharacteristics. For example, if amplifiers connected to the output endsof compensation waveguides 225 _(m+n), 225 _(m+n−1), 225 _(m+n−2), . . .do not have flat output characteristics, then it is necessary to designtotal output characteristics in view of the output characteristics ofthe amplifiers. Actually, therefore, the intensities of optical signalsobtained by compensation waveguides 225 _(m+n), 225 _(m+n−1), 225_(m+n−2), . . . are compensated for according to the outputcharacteristics that are needed.

Modifications of 1st Through 5th Embodiments

FIG. 19 shows a general input/output relationship of a slab waveguide ofan arrayed waveguide grating. In FIG. 19, those parts identical to thoseshown in FIG. 2 are denoted by identical reference numerals. In thefirst embodiment, optical signals from channel waveguide array 102 enteroutput slab waveguide 101, and demultiplexed optical signals are outputfrom respective waveguides 104 of output waveguides 105. Conversely,waveguides 104 of output waveguides 105 may be used as input waveguides,and channel waveguide array 102 may be used as an output waveguide formultiplexing optical signals of various wavelengths or signals.Heretofore, it has been necessary to adjust the intensity levels oflight at the input stage because the intensity levels of light enteringfrom a relatively central region of output waveguides 105 are high. Withoutput slab waveguide 101 according to the first embodiment being usedas an inverted input/output configuration, such intensity levels do notneed to be adjusted, and the signal levels of multiplexed signals can bebrought into an appropriate range.

The arrangement for multiplying optical signals using the arrayedwaveguide grating according to the first embodiment has been describedabove. However, the configuration shown in FIG. 19 is also applicable tothe arrayed waveguide gratings according to the second through fifthembodiments for using these arrayed waveguide gratings as multiplexersfor optical signals as well as demultiplexers for optical signals.

6th Embodiment

FIG. 20 shows in block form a demultiplexer according to a sixthembodiment of the present invention. As shown in FIG. 20, thedemultiplexer, denoted by 301, has a waveguide device 303 for beingsupplied with optical signal 302. Waveguide device 303 may be any of thearrayed waveguide gratings according to the first through fifthembodiments. Waveguide device 303 demultiplexes a coupled optical signaland outputs demultiplexed optical signals 305 ₁ through 305 _(N) fromrespective output waveguides 304 ₁ through 304 _(N). Monitoringamplifiers 306 ₁ through 306 _(N) are connected to the respective outputends of output waveguides 304 ₁ through 304 _(N). Monitoring amplifiers306 ₁ through 306 _(N) serve as AGC (Automatic Gain Control) circuitsfor detecting signal levels of corresponding optical signals 305 ₁through 305 _(N) and amplifying or attenuating them to desired levels.Thus, optical signals 305 ₁ through 305 _(N) whose gains have beeninitially adjusted by waveguide device 303 are finally adjusted in gainby monitoring amplifiers 306 ₁ through 306 _(N), and output as opticalsignals 307 ₁ through 307 _(N) therefrom.

While it is possible for waveguide device 303 to make flat the levels ofoptical signals 305 ₁ through 305 _(N), monitoring amplifiers 306 ₁through 306 _(N) are capable of adjusting the levels thereof even if theoutput characteristics of demultiplexer 301 as a whole are differentfrom that of waveguide device 303.

7th Embodiment

FIG. 21 shows in block form a multiplexer according to a seventhembodiment of the present invention. As shown in FIG. 21, themultiplexer, denoted by 301, has a plurality of semiconductor lasers 322₁ through 322 _(N) for outputting optical signals of plural wavelengths.Optical signals 323 ₁ through 323 _(N) output from respectivesemiconductor lasers 322 ₁ through 322 _(N) are divided by dividers 324₁ through 324 _(N) into two groups of optical signals. Optical signals325 ₁ through 325 _(N) of one group couple to waveguide device 326,which multiplexes optical signals 325 ₁ through 325 _(N) into opticalsignal 327 and outputs multiplexed optical signal 327.

Optical signals 328 ₁ through 328 _(N) of the other group which aredivided by dividers 324 ₁ through 324 _(N) have their signal levelsdetected by respective level detectors 329 ₁ through 329 _(N), which maycomprise photodiodes. Based on detected results from level detectors 329₁ through 329 _(N), drive controllers 331 ₁ through 331 _(N) associatedwith respective semiconductor lasers 322 ₁ through 322 _(N) controloutput levels of laser beams emitted therefrom. As a result, the levelsof the optical signals of respective wavelengths, which make up opticalsignal 327 output from waveguide device 326, can be set to appropriatelevels.

If waveguide device 326 has its output characteristics compensated forto output a multiplexed signal whose level is equal to the equal levelsof the optical signals coupled thereto, then the output characteristicsof the multiplexer 321 can be made flat without the use of drivecontrollers 331 ₁ through 331 _(N). However, drive controllers 331 ₁through 331 _(N) are capable of adjusting output characteristics if themultiplexer 321 is required to have different output characteristics ormake highly accurate level adjustments.

8th Embodiment

FIG. 22 shows in block form an optical communication system according toan eighth embodiment of the present invention. The optical communicationsystem has optical multiplexer (MUX) 402 which multiplexes opticalsignals of N channels having respective wavelengths λ₁ through λ_(N)transmitted from optical transmitter 401 connected to a SONET(Synchronous Optical Network) system, not shown. A multiplexed opticalsignal 405 is amplified by booster amplifier 403 and delivered intooptical transmission path 404. Optical multiplexer 402 comprise thearrayed waveguide grating according to the first embodiment. Multiplexedoptical signal 405 is then amplified by in-line amplifiers 406, andapplied via preamplifier 407 to optical demultiplexer (DMUX) 408, whichdemultiplexes multiplexed optical signal 405 into original opticalsignals having respective wavelengths λ₁ through λ_(N), which arereceived by optical receiver 409. Optical transmission path 404 betweenin-line amplifiers 406 has a suitable number of nodes (OADM) 411 ₁through 411 _(M). Optical signals of desired wavelengths are input toand output from these nodes 411 ₁ through 411 _(M).

FIG. 23 shows a node in block form. While first node 411 ₁ is shown inFIG. 23, second through Mth nodes 411 ₂ through 411 _(M) are identicalin structure to first node 411 ₁. Optical signal transmitted overtransmission path 404 shown in FIG. 22 is applied to input arrayedwaveguide grating (AWG) 421 of first node 411 ₁, which demultiplexes theoptical signal into optical signals of N channels having respectivewavelengths λ₁ through λ_(N). The optical signals having respectivewavelengths λ₁ through λ_(N) are dropped into node receivers 426 by2-input, 2-output optical switches 422 ₁ through 422 _(N) associatedwith respective wavelengths λ₁ through λ_(N), and optical signalstransmitted from node transmitters 424 are added to the optical signalshaving respective wavelengths λ₁ through λ_(N). Optical signals outputfrom 2-input, 2-output optical switches 422 ₁ through 422 _(N) are alsodirectly input to output arrayed waveguide grating 428. Output arrayedwaveguide grating 428 is a device which is a structural reversal ofinput arrayed waveguide grating 421, and multiplexes optical signals ofN channels having respective wavelengths λ₁ through λ_(N) into opticalsignal 420 ₅, which is transmitted over an optical transmission path404.

Heretofore, attenuators for respective wavelengths λ₁ through λ_(N) areconnected between 2-input, 2-output optical switches 422 ₁ through 422_(N) and output arrayed waveguide grating 428 for eliminating signallevel irregularities caused when multiplexed optical signal 405 passesthrough input arrayed waveguide grating 421 and signal levelirregularities of optical signal 405 for respective wavelengths λ₁through λ_(N) which have been multiplexed by output arrayed waveguidegrating 428. In the optical communication system according to the eighthembodiment, as described above with respect to the first embodiment andthe modification of the first through fifth embodiments, input arrayedwaveguide grating 421 and output arrayed waveguide grating 428 arecapable of compensating for level variations between the waveguides. Inthe present embodiment, therefore, attenuators which have heretoforebeen required in applications where dynamic level compensation is notneeded are not employed, and the requirement for dynamic rangecharacteristics of the level compensators is reduced in applicationswhere dynamic level compensation is needed.

First node 4111 shown in FIG. 23, and second through Mth nodes 411 ₂through 411 _(M), optical multiplexer 402, and optical demultiplexer 408shown in FIG. 22 employ arrayed waveguide gratings. Therefore, in viewof a demand for an increased number of channels N for optical signal405, it is important to stabilize the wavelengths of laser beams andmonitor the output levels of the laser beams which are output inmultiple channels from the output slab waveguides of the arrayedwaveguide gratings. As shown in FIG. 22, nodes 411 ₁ through 4111 _(M)and optical transmitter 401 are associated with respective outputmonitoring control devices 431 ₁ through 431 _(S).

Modifications of 8th Embodiment

The eighth embodiment described above uses the arrayed waveguide gratingaccording to the first embodiment. However, each of the arrayedwaveguide gratings according to the second through fifth embodiments maybe used in place of the arrayed waveguide grating according to the firstembodiment in the eighth embodiment, providing a similar opticalcommunication system. Furthermore, the multiplexer and the demultiplexeraccording to the sixth and seventh embodiments may be used instead ofthe above arrayed waveguide gratings.

Supplemental Description

The preferred embodiments of the present invention have been describedabove. According to the present invention, desired optical input/outputcharacteristics are achieved by producing optical losses in the slabwaveguide of the arrayed waveguide grating or the waveguide connectedthereto (including individual waveguides of the channel waveguidearray). One approach to achieving such desired optical input/outputcharacteristics is to use the degree of matching of a focal point (9thand 10th aspects). The concept of a focal point in an arrayed waveguidegrating will be described below.

FIG. 24 shows the manner in which coherent light emitted from a lightsource is propagated. When light is emitted to the left in FIG. 24 frompoint light source 501, the light is spread with a cophasal surface asindicated by the dotted lines. Since all points on the cophasal surfaceare always spaced an equal distance from point light source 501, thecophasal surface is concentric to point light source 501.

If light whose cophasal surface is arcuate is radiated from the left tothe right in FIG. 24, then it propagates in the opposite direction andis focused at point light source 501, which serves as a focal point.While point light source 501 does not exist in reality, if a lightsource can be regarded as being positioned sufficiently far in view ofoptical radiation and convergence, then a light source having a width ora length can be handled as point light source 501.

For example, channel waveguide array 15 shown in FIG. 1 is of astructure for confining light three-dimensionally with the corevertically sandwiched by the cladding layer. If such a channel waveguidearray is positioned far enough, then it can be handled as point lightsource 501 and radiation and convergence of light emitted therefrom canbe considered. In an arrayed waveguide grating, the exit of the channelwaveguide array is disposed in a circumferential pattern. If thewaveguides are cophasal at the exit of the channel waveguide array, thenit is possible to generate light whose cophasal surface is approximatelyin a circumferential pattern and emit the light toward the center of thecircumferential pattern. Thus, a focal point can be provided at thecenter of the circumferential pattern.

Even if the waveguides are not cophasal at the exit of the channelwaveguide array, a focal point is provided at a position off the centerof the circumferential pattern if the waveguides are out of phase witheach other. With a demultiplexer-type arrayed waveguide grating, thewavelengths propagated through the respective waveguides of the channelwaveguide array are out of phase with each other. Therefore, the opticalsignals of different wavelengths each other are focused at differentpositions in the output slab waveguide.

With a multiplexer-type arrayed waveguide grating, it is preferable tofocus the optical signals of different wavelengths each other at thesame position regardless of the different wavelengths each other. Inthis case, the positions where the optical signals are applied need tobe changed depending on the wavelength thereof in order to cancel phasedifferences caused when the optical signals are propagated through thechannel waveguide array.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the appended claims.

1. An optical communication system comprising: optical transmittingmeans for transmitting optical signals of respective wavelengthsparallel to each other; a multiplexer for wavelength-divisionmultiplexing the optical signals of respective wavelengths transmittedby said optical transmitting means; an optical transmission path fortransmitting a wavelength-division multiplexed optical signal outputfrom said multiplexer; a node disposed in said optical transmission pathand having an arrayed waveguide grating; a demultiplexer for beingsupplied with the optical signal transmitted over said opticaltransmission path via said node and demultiplexing the optical signalinto the optical signals of respective wavelengths; and opticalreceiving means for receiving the optical signals of respectivewavelengths demultiplexed by said demultiplexer, wherein saidmultiplexer comprises an arrayed waveguide grating comprising: aplurality of input waveguides for inputting signal lights havingdifferent wavelengths from a light source; one or plural outputwaveguides for outputting signal lights; a channel waveguide arrayhaving waveguides which are successively longer with predeterminedwaveguide length differences; an output slab waveguide connecting anoutput end of said channel waveguide array to said output waveguides;and an input slab waveguide connecting an input end of said channelwaveguide array to said input waveguides, and having opticalinput/output characteristics set to predetermined ratios for therespective input waveguides with respect to the output waveguides,wherein said output waveguides are configured such that an output levelof said signal lights is adjusted in the arrayed waveguide grating ofsaid multiplexer, wherein said demultiplexer comprises an arrayedwaveguide grating comprising: one or plural input waveguides forinputting signal lights; a plurality of output waveguides for outputtingsignal lights; a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences; aninput slab waveguide connecting an input end of said channel waveguidearray to said input waveguides; and an output slab waveguide connectingan output end of said channel waveguide array to said output waveguides,and having optical input/output characteristics set to predeterminedratios for the respective output waveguides with respect to said inputwaveguides, wherein said output waveguides are configured such that anoutput level of said signal lights is adjusted in the arrayed waveguidegrating of said demultiplexer, and wherein a central axis of at leastone of said output waveguides are out of alignment with a remainder ofsaid output waveguides.
 2. An optical communication system comprising:optical transmitting means for transmitting optical signals ofrespective wavelengths parallel to each other; a multiplexer forwavelength-division multiplexing the optical signals of respectivewavelengths transmitted by said optical transmitting means; an opticaltransmission path for transmitting a wavelength-division multiplexedoptical signal output from said multiplexer; a node disposed in saidoptical transmission path and having an arrayed waveguide grating; ademultiplexer for being supplied with the optical signal transmittedover said optical transmission path via said node and demultiplexing theoptical signal into the optical signals of respective wavelengths; andoptical receiving means for receiving the optical signals of respectivewavelengths demultiplexed by said demultiplexer, wherein saidmultiplexer comprises an arrayed waveguide grating comprising: aplurality of input waveguides for inputting signal lights havingdifferent wavelengths; one or plural output waveguides for outputtingsignal lights; a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences; anoutput slab waveguide connecting an output end of said channel waveguidearray to said output waveguides; and an input slab waveguide connectingan input end of said channel waveguide array to said input waveguides,and having optical input/output characteristics set to predeterminedratios for the respective input waveguides with respect to the outputwaveguides depending on the differences between optical losses alongrespective paths in the output slab waveguide, wherein said outputwaveguides are configured such that an output level of said signallights is adjusted in the arrayed waveguide grating of said multiplexer,wherein said demultiplexer comprises an arrayed waveguide gratingcomprising: one or plural input waveguides for inputting signal lights;a plurality of output waveguides for outputting signal lights; a channelwaveguide array having waveguides which are successively longer withpredetermined waveguide length differences; an input slab waveguideconnecting an input end of said channel waveguide array to said inputwaveguides; and an output slab waveguide connecting an output end ofsaid channel waveguide array to said output waveguides, and havingoptical input/output characteristics set to predetermined ratios for therespective output waveguides with respect to said input waveguidesdepending on the differences between optical losses along respectivepaths in the output slab waveguide, wherein said output waveguides areconfigured such that an output level of said signal lights is adjustedin the arrayed waveguide grating of said demultiplexer, and wherein acentral axis of at least one of said output waveguides are out ofalignment with a remainder of said output waveguides.
 3. An opticalcommunication system comprising: an annular transmission path having aplurality of nodes interconnected in a ring by a transmission path, fortransmitting a wavelength-division multiplexed optical signal over thetransmission path; each of said nodes having a first arrayed waveguidegrating for demultiplexing a wavelength-division multiplexed opticalsignal into optical signals of respective wavelengths, and a secondarrayed waveguide grating for wavelength-division multiplexing thedemultiplexed optical signals of respective wavelengths, wherein saidfirst arrayed waveguide grating comprises: one or plural inputwaveguides for inputting signal lights; a plurality of output waveguidesfor outputting signal lights; a channel waveguide array havingwaveguides which are successively longer with predetermined waveguidelength differences; an input slab waveguide connecting an input end ofsaid channel waveguide array to said input waveguides; and an outputslab waveguide connecting an output end of said channel waveguide arrayto said output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to said input waveguides, wherein said outputwaveguides are configured such that an output level of said signallights is adjusted in the first arrayed waveguide grating, wherein saidsecond arrayed waveguide grating comprises: a plurality of inputwaveguides for inputting signal lights having different wavelengths eachother; one or plural output waveguides for outputting signal lights; achannel waveguide array having waveguides which are successively longerwith predetermined waveguide length differences; an output slabwaveguide connecting an output end of said channel waveguide array tosaid output waveguides; and an input slab waveguide connecting an inputend of said channel waveguide array to said input waveguides, and havingoptical input/output characteristics set to predetermined ratios for therespective input waveguides corresponding to the output waveguides,wherein said output waveguides are configured such that an output levelof said signal lights is adjusted in the second arrayed waveguidegrating, and wherein a central axis of at least one of said outputwaveguides are out of alignment with a remainder of said outputwaveguides.
 4. An optical communication system comprising: an annulartransmission path having a plurality of nodes interconnected in a ringby a transmission path, for transmitting a wavelength-divisionmultiplexed optical signal over the transmission path, wherein each ofsaid nodes having a first arrayed waveguide grating for demultiplexing awavelength-division multiplexed optical signal into optical signals ofrespective wavelengths, and a second arrayed waveguide grating formultiplexing the demultiplexed optical signals of respectivewavelengths, wherein said first arrayed waveguide grating comprises: oneor plural input waveguides for inputting signal lights; a plurality ofoutput waveguides for outputting signal lights; a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences; an input slab waveguide connecting aninput end of said channel waveguide array to said input waveguides; andan output slab waveguide connecting an output end of said channelwaveguide array to said output waveguides, and having opticalinput/output characteristics set to predetermined ratios for therespective output waveguides with respect to said input waveguidesdepending on the differences between optical losses along respectivepaths in the output slab waveguide, wherein said output waveguides areconfigured such that an output level of said signal lights is adjustedin the first arrayed waveguide grating, wherein said second arrayedwaveguide grating comprises: a plurality of input waveguides forinputting signal lights having different wavelengths each other; one orplural output waveguides for outputting signal lights; a channelwaveguide array having waveguides which are successively longer withpredetermined waveguide length differences; an output slab waveguideconnecting an output end of said channel waveguide array to said outputwaveguides; and an input slab waveguide connecting an input end of saidchannel waveguide array to said input waveguides, and having opticalinput/output characteristics set to predetermined ratios for therespective input waveguides corresponding to the output waveguidesdepending on the differences between optical losses along respectivepaths in the output slab waveguide, wherein said output waveguides areconfigured such that an output level of said signal lights is adjustedin the second arrayed waveguide grating, and wherein a central axis ofat least one of said output waveguides are out of alignment with aremainder of said output waveguides.
 5. An optical communication systemcomprising: optical transmitting means for transmitting optical signalsof respective wavelengths parallel to each other; a multiplexer forwavelength-division multiplexing the optical signals of respectivewavelengths transmitted by said optical transmitting means; an opticaltransmission path for transmitting a wavelength-division multiplexedoptical signal output from said multiplexer; a node disposed in saidoptical transmission path; a demultiplexer for being supplied with theoptical signal transmitted over said optical transmission path via saidnode and demultiplexing the optical signal into the optical signals ofrespective wavelengths; and optical receiving means for receiving theoptical signals of respective wavelengths demultiplexed by saiddemultiplexer, wherein said multiplexer comprises an arrayed waveguidegrating comprising: a plurality of input waveguides for inputting signallights having different wavelengths; one or plural output waveguides foroutputting signal lights; a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an output slab waveguide connecting an output end of saidchannel waveguide array to said output waveguides; an input slabwaveguide connecting an input end of said channel waveguide array tosaid input waveguides, and having optical input/output characteristicsset to predetermined ratios for the respective input waveguidescorresponding to the output waveguides; and level detecting means fordetecting levels of the signal lights input to said arrayed waveguidegrating; and level adjusting means for comparing the levels of thesignal lights detected by said level detecting means with predeterminedlevels for the respective wavelengths, and adjusting output levels ofthe light signals to set the levels of the waveguides multiplexed bysaid arrayed waveguide grating to desired values, and wherein saiddemultiplexer comprises an arrayed waveguide grating comprising: one orplural input waveguides for inputting signal lights; a plurality ofoutput waveguides for outputting signal light; a channel waveguide arrayhaving waveguides which are successively longer with predeterminedwaveguide length differences; an input slab waveguide connecting aninput end of said channel waveguide array to said input waveguides; anoutput slab waveguide connecting an output end of said channel waveguidearray to said output waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective outputwaveguides with respect to said input waveguides; and level adjustingmeans for being supplied with the signal lights of respectivewavelengths from the output waveguides of said arrayed waveguidegrating, and adjusting output levels of said signal lights to desiredvalues.
 6. An optical communication system comprising: opticaltransmitting means for transmitting optical signals of respectivewavelengths parallel to each other; a multiplexer forwavelength-division multiplexing the optical signals of respectivewavelengths transmitted by said optical transmitting means; an opticaltransmission path for transmitting a wavelength-division multiplexedoptical signal output from said multiplexer; a node disposed in saidoptical transmission path; a demultiplexer for being supplied with theoptical signal transmitted over said optical transmission path via saidnode and demultiplexing the optical signal into the optical signals ofrespective wavelengths; and optical receiving means for receiving theoptical signals of respective wavelengths demultiplexed by saiddemultiplexer, wherein said multiplexer comprises an arrayed waveguidegrating comprising: a plurality of input waveguides for inputting signallights having different wavelengths; one or plural output waveguides foroutputting signal lights; a channel waveguide array having waveguideswhich are successively longer with predetermined waveguide lengthdifferences; an output slab waveguide connecting an output end of saidchannel waveguide array to said output waveguides; an input slabwaveguide connecting an input end of said channel waveguide array tosaid input waveguides, and having optical input/output characteristicsset to predetermined ratios for the respective input waveguidescorresponding to the output waveguides depending on the differencesbetween optical losses along respective paths in the output slabwaveguide; level detecting means for detecting levels of the signallights input to said arrayed waveguide grating; and level adjustingmeans for comparing the levels of the signal lights detected by saidlevel detecting means with predetermined levels for the respectivewavelengths, and adjusting output levels of the signal lights to set thelevels of the waveguides multiplexed by said arrayed waveguide gratingto desired values, and wherein said demultiplexer comprises an arrayedwaveguide grating comprising: one or plural input waveguides forinputting signal lights; a plurality of output waveguides for outputtingsignal lights; a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences; aninput slab waveguide connecting an input end of said channel waveguidearray to said input waveguides; an output slab waveguide connecting anoutput end of said channel waveguide array to said output waveguides,and having optical input/output characteristics set to predeterminedratios for the respective output waveguides with respect to said inputwaveguides depending on the differences between optical losses alongrespective paths in the output slab waveguide; and level adjusting meansfor being supplied with the signal lights of respective wavelengths fromthe output waveguides of said arrayed waveguide grating, and adjustingoutput levels of said signal lights to desired values.
 7. An opticalcommunication system comprising: an annular transmission path having aplurality of nodes interconnected in a ring by a transmission path, fortransmitting a wavelength-division multiplexed optical signal over thetransmission path, wherein each of said nodes having a demultiplexer fordemultiplexing a wavelength-division multiplexed optical signal intooptical signals of respective wavelengths, and a multiplexer forwavelength-division multiplexing the demultiplexed optical signals ofrespective wavelengths, wherein said demultiplexer comprising an arrayedwaveguide grating comprising: one or plural input waveguides forinputting signal lights; a plurality of output waveguides for outputtingsignal lights; a channel waveguide array having waveguides which aresuccessively longer with predetermined waveguide length differences; aninput slab waveguide connecting an input end of said channel waveguidearray to said input waveguides; an output slab waveguide connecting anoutput end of said channel waveguide array to said output waveguides,and having optical input/output characteristics set to predeterminedratios for the respective output waveguides with respect to said inputwaveguides; and level adjusting means for being supplied with the signallights of respective wavelengths from the output waveguides of saidarrayed waveguide grating, and adjusting output levels of said signallights to desired values, and wherein said multiplexer comprises anarrayed waveguide grating comprising: a plurality of input waveguidesfor inputting signal lights having different wavelengths; one or pluraloutput waveguides for outputting signal lights; a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences; an output slab waveguide connecting anoutput end of said channel waveguide array to said output waveguides; aninput slab waveguide connecting an input end of said channel waveguidearray to said input waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective inputwaveguides corresponding to the output waveguides; level detecting meansfor detecting levels of the signal lights input to said arrayedwaveguide grating; and level adjusting means for comparing the levels ofthe signal lights detected by said level detecting means withpredetermined levels for the respective wavelengths, and adjustingoutput levels of the light signals to set the levels of the waveguidesmultiplexed by said arrayed waveguide grating to desired values.
 8. Anoptical communication system comprising: an annular transmission pathhaving a plurality of nodes interconnected in a ring by a transmissionpath, for transmitting a wavelength-division multiplexed optical signalover the transmission path, wherein each of said nodes having ademultiplexer for demultiplexing a wavelength-division multiplexedoptical signal into optical signals of respective wavelengths, and amultiplexer for frequency-division multiplexing the demultiplexedoptical signals of respective wavelengths, wherein said demultiplexercomprises an arrayed waveguide grating comprising: one or plural inputwaveguides for inputting signal lights; a plurality of output waveguidesfor outputting signal lights; a channel waveguide array havingwaveguides which are successively longer with predetermined waveguidelength differences; an input slab waveguide connecting an input end ofsaid channel waveguide array to said input waveguides; an output slabwaveguide connecting an output end of said channel waveguide array tosaid output waveguides, and having optical input/output characteristicsset to predetermined ratios for the respective output waveguides withrespect to said input waveguides depending on the differences betweenoptical losses along respective paths in the output slab waveguide;level adjusting means for being supplied with the signal lights ofrespective wavelengths from the output waveguides of said arrayedwaveguide grating, and adjusting output levels of said signal lights todesired values, and wherein said multiplexer comprising an arrayedwaveguide grating comprising: a plurality of input waveguides forinputting signal lights having different wavelengths; one or pluraloutput waveguides for outputting signal lights; a channel waveguidearray having waveguides which are successively longer with predeterminedwaveguide length differences; an output slab waveguide connecting anoutput end of said channel waveguide array to said output waveguides; aninput slab waveguide connecting an input end of said channel waveguidearray to said input waveguides, and having optical input/outputcharacteristics set to predetermined ratios for the respective inputwaveguides corresponding to the output waveguides depending on thedifferences between optical losses along respective paths in the outputslab waveguide; level detecting means for detecting levels of the signallights input to said arrayed waveguide grating; and level adjustingmeans for comparing the levels of the signal lights detected by saidlevel detecting means with predetermined levels for the respectivewavelengths, and adjusting output levels of the signal lights to set thelevels of the waveguides multiplexed by said arrayed waveguide gratingto desired values.
 9. An optical communication system comprising:optical transmitting means for transmitting optical signals ofrespective wavelengths parallel to each other; a multiplexer forwavelength-division multiplexing the optical signals of respectivewavelengths transmitted by said optical transmitting means; an opticaltransmission path for transmitting a wavelength-division multiplexedoptical signal output from said multiplexer; a node disposed in saidoptical transmission path and having a waveguide device; a demultiplexerfor being supplied with the optical signal transmitted over said opticaltransmission path via said node and demultiplexing the optical signalinto the optical signals of respective wavelengths; and opticalreceiving means for receiving the optical signals of respectivewavelengths demultiplexed by said demultiplexer, wherein saidmultiplexer comprises: a plurality of input waveguides for inputtingsignal lights; one or plural output waveguides for outputting signallights; and a slab waveguide having optical input/output characteristicsset to predetermined ratios for the respective input waveguides withrespect to the output waveguides, wherein said output waveguides areconfigured such that an output level of said signal lights is adjustedin the arrayed waveguide grating of said multiplexer, wherein saiddemultiplexer comprises a waveguide device comprising: one or pluralinput waveguides for inputting signal lights; a plurality of outputwaveguides for outputting signal lights; and a slab waveguide havingoptical input/output characteristics set to predetermined ratios for therespective output waveguides with respect to said input waveguides,wherein said output waveguides are configured such that an output levelof said signal lights is adjusted in the arrayed waveguide grating ofsaid demultiplexer, and wherein a central axis of at least one of saidoutput waveguides are out of alignment with a remainder of said outputwaveguides.
 10. An optical communication system comprising: an annulartransmission path having a plurality of nodes interconnected in a ringby a transmission path, for transmitting a wavelength-divisionmultiplexed optical signal over the transmission path, wherein each ofsaid nodes having a first waveguide device for demultiplexing awavelength-division multiplexed optical signal into optical signals ofrespective wavelengths, and a second waveguide device forwavelength-division multiplexing the demultiplexed optical signals ofrespective wavelengths, wherein said first waveguide device comprising:one or plural input waveguides for inputting signal lights; a pluralityof output waveguides for outputting signal lights; and a slab waveguidehaving optical input/output characteristics set to predetermined ratiosfor the respective output waveguides with respect to said inputwaveguides, wherein said output waveguides are configured such that anoutput level of said signal lights is adjusted in the arrayed waveguidegrating of said multiplexer, wherein said second waveguide devicecomprises: a plurality of input waveguides for inputting signal lights;one or plural output waveguides for outputting signal lights; and a slabwaveguide having optical input/output characteristics set topredetermined ratios for the respective input waveguides with respect tothe output waveguides, wherein said output waveguides are configuredsuch that an output level of said signal lights is adjusted in thearrayed waveguide grating of said demultiplexer, and wherein a centralaxis of at least one of said output waveguides are out of alignment witha remainder of said output waveguides.
 11. An optical communicationsystem comprising: optical transmitting means for transmitting opticalsignals of respective wavelengths parallel to each other; a multiplexerfor wavelength-division multiplexing the optical signals of respectivewavelengths transmitted by said optical transmitting means; an opticaltransmission path for transmitting a wavelength-division multiplexedoptical signal output from said multiplexer; a node disposed in saidoptical transmission path; a demultiplexer for being supplied with theoptical signal transmitted over said optical transmission path via saidnode and demultiplexing the optical signal into the optical signals ofrespective wavelengths; and optical receiving means for receiving theoptical signals of respective wavelengths demultiplexed by saiddemultiplexer, wherein said multiplexer comprises a plurality of lightsources for respective signals, and a waveguide device comprising: aplurality of input waveguides for inputting signal lights; one or pluraloutput waveguides for outputting signal lights; and a slab waveguidehaving optical input/output characteristics set to predetermined ratiosfor the respective input waveguides with respect to the outputwaveguides; level detecting means for detecting levels of the signallights input from said light sources to said waveguide device; and leveladjusting means for comparing the levels of the signal lights detectedby said level detecting means with predetermined levels for therespective signal lights, and adjusting output levels of the respectivesignal lights to set the levels of the signal lights multiplexed by saidwaveguide device to desired values, and wherein said demultiplexercomprising a waveguide device comprising: one or plural input waveguidesfor inputting signal lights; a plurality of output waveguides foroutputting signal lights; and a slab waveguide having opticalinput/output characteristics set to predetermined ratios for therespective output waveguides with respect to the input waveguides; andlevel adjusting means for being supplied with the signal lights from theoutput waveguides of said waveguide device, and adjusting output levelsof said signal lights to desired values.
 12. An optical communicationsystem comprising: an annular transmission path having a plurality ofnodes interconnected in a ring by a transmission path, for transmittinga wavelength-division multiplexed optical signal over the transmissionpath, wherein each of said nodes having a demultiplexer fordemultiplexing a multiplexed optical signal into optical signals ofrespective wavelengths, and a multiplexer for wavelength-divisionmultiplexing the demultiplexed optical signals of respectivewavelengths, wherein said demultiplexer comprises a waveguide devicecomprising: one or plural input waveguides for inputting signal lights;a plurality of output waveguides for outputting signal lights; and aslab waveguide having optical input/output characteristics set topredetermined ratios for the respective output waveguides with respectto the input waveguides; and level adjusting means for being suppliedwith the signal lights from the output waveguides of said waveguidedevice, and adjusting output levels of said signal lights to desiredvalues, and wherein said multiplexer comprises a plurality of lightsources for respective signals, and a waveguide device comprising: aplurality of input waveguides for inputting signal lights; one or pluraloutput waveguides for outputting signal lights; and a slab waveguidehaving optical input/output characteristics set to predetermined ratiosfor the respective input waveguides with respect to the outputwaveguides; level detecting means for detecting levels of the signallights input from said light sources to said waveguide device; and leveladjusting means for comparing the levels of the signal lights detectedby said level detecting means with predetermined levels for therespective signal lights, and adjusting output levels of the respectivesignal lights to set the levels of the signal lights multiplexed by saidwaveguide device to desired values.
 13. The optical communication systemof claim 1, wherein said input slab waveguide of said multiplexercomprises a core layer disposed therein for propagating lighttherethrough, said core layer being partly cut off in selected pathstherein, which interconnect said channel waveguide array and saidplurality of input waveguides.
 14. The optical communication system ofclaim 1, wherein said output slab waveguide of said demultiplexerincludes a core layer disposed therein for propagating lighttherethrough, said core layer being partly cut off in selected pathstherein, which interconnect said channel waveguide array and saidplurality of output waveguides.
 15. The optical communication system ofclaim 1, wherein a central axis of a selected output waveguide isdisplaced along a direction perpendicular to said central axis of saidselected output waveguide from a corresponding focusing position by apredetermined value to attenuate said signal light intensity.
 16. Theoptical communication system of claim 1, wherein a central axis of aselected output waveguide is inclined from a perpendicular to a surfaceof an output end of said output waveguide at a focusing position toattenuate said signal light intensity.
 17. The optical communicationsystem of claim 1, wherein a diameter of a selected output waveguide ischanged at a focusing position to adjust said signal light intensity.18. The optical communication system of claim 1, wherein said output endof said output slab waveguide partially projects toward ends of selectedoutput waveguides from a cophasal plane of corresponding focusingpositions, an end of a selected output waveguide is displaced along itpropagation axis by a shifted focus distance in a direction away fromsaid cophasal plane to attenuate said signal light intensity.
 19. Theoptical communication system of claim 1, wherein said input slabwaveguide of said multiplexer includes a cladding layer being disposedin cut regions of said core layer and on opposite sides of said corelayer, said cut regions in said selected optical paths including cutlengths set to predetermined values in a direction in which said signallights propagate to attenuate said signal light intensity.
 20. Theoptical communication system of claim 13, wherein said output slabwaveguide of said demultiplexer includes a cladding layer being disposedin cut regions of said core layer and on opposite sides of said corelayer, said cut regions in said selected optical paths including cutlengths set to predetermined values in a direction in which said signallights propagate to attenuate said signal light intensity.
 21. Theoptical communication system according to claim 1, wherein said outputwaveguide comprises ports that are disposed with a displaced angularspacing.
 22. The optical communication system according to claim 5,wherein said level adjusting means in said multiplexer comprises aconfiguration of said output waveguides in said multiplexer, and whereinsaid level adjusting means in said demultiplexer comprises aconfiguration of said output waveguides in said demultiplexer.